diff --git a/.npmignore b/.npmignore
new file mode 100644
index 0000000..4339d3f
--- /dev/null
+++ b/.npmignore
@@ -0,0 +1,3 @@
+yarn.lock
+examples/
+tests.js
diff --git a/package.json b/package.json
index ebe3770..b5fea00 100644
--- a/package.json
+++ b/package.json
@@ -5,9 +5,9 @@
   "version": "0.6.3",
   "dependencies": {},
   "devDependencies": {
-    "mocha": "1.7.0",
+    "mocha": "^3.5.0",
     "pre-commit": "^1.0.5",
-    "should": "1.2.1"
+    "should": "^12.0.0"
   },
   "maintainers": [
     "Samuel Reed <sam@tixelated.com>",
diff --git a/tests.js b/tests.js
index 8f0c366..5b00dcb 100644
--- a/tests.js
+++ b/tests.js
@@ -12,11 +12,11 @@ function tightWork(duration) {
 /*global describe, it, beforeEach, afterEach */
 describe('the library', function() {
   it('should export a couple functions', function() {
-    (toobusy).should.be.a('function');
-    (toobusy.maxLag).should.be.a('function');
-    (toobusy.shutdown).should.be.a('function');
-    (toobusy.interval).should.be.a('function');
-    (toobusy.shutdown).should.be.a('function');
+    should(toobusy).be.Function();
+    (toobusy.maxLag).should.be.Function();
+    (toobusy.shutdown).should.be.Function();
+    (toobusy.interval).should.be.Function();
+    (toobusy.shutdown).should.be.Function();
     (toobusy).should.not.have.property('start');
   });
   it('should start automatically', function() {
@@ -61,9 +61,9 @@ describe('toobusy()', function() {
   // is nice for making these tests independent of each other.
   beforeEach(function() {
     toobusy.maxLag(10);
-    toobusy.interval(250);
+    toobusy.interval(50);
   });
-  afterEach(function() {
+  after(function() {
     toobusy.maxLag(70);
     toobusy.interval(500);
   });
@@ -97,49 +97,50 @@ describe('toobusy()', function() {
     it('should not emit lag events if the lag is less than the configured threshold',
         testLagEvent(100, 50, false));
     it('should emit lag events if the lag is greater than the configured threshold',
-        testLagEvent(50, 100, true));
+        testLagEvent(50, 150, true));
     it('should emit lag events if lag occurs and no threshold is specified',
         testLagEvent(undefined, 500, true));
 
     function testLagEvent(threshold, work, expectFire) {
       return function (done) {
         var calledDone = false;
+        var finish = function() {
+          if (calledDone) return;
+          calledDone = true;
+          toobusy.shutdown(); // stops onLag() from firing again
+          clearTimeout(workTimeout);
+          done.apply(null, arguments);
+        };
 
         toobusy.onLag(function (lag) {
-          if (calledDone) {
-            return;
-          }
-
           if (!expectFire) {
-            calledDone = true;
-            done(new Error('lag event fired unexpectedly'));
-            return;
+            return finish(new Error('lag event fired unexpectedly'));
           }
 
           should.exist(lag);
           lag.should.be.above(threshold || 0);
-
-          calledDone = true;
-          done();
+          finish();
         }, threshold);
 
         if (!expectFire) {
           setTimeout(function () {
-            if (!calledDone) {
-              calledDone = true;
-              done();
-            }
+            finish();
           }, work + threshold);
         }
 
-        tightWork(work);
+        // Do work 3x to work around smoothing factor
+        var count = 0;
+        var workTimeout = setTimeout(function working() {
+          tightWork(work);
+          if (++count < 3) workTimeout = setTimeout(working);
+        })
       }
     }
   });
 });
 
 describe('smoothingFactor', function() {
-  //Sometimes the default 2s timeout is hit on this suite, raise to 10s.
+  // Sometimes the default 2s timeout is hit on this suite, raise to 10s.
   this.timeout(10 * 1000);
 
   beforeEach(function() {
@@ -147,7 +148,7 @@ describe('smoothingFactor', function() {
     toobusy.maxLag(10);
     toobusy.interval(250);
   });
-  afterEach(function() {
+  after(function() {
     toobusy.maxLag(70);
     toobusy.interval(500);
   });
@@ -204,22 +205,19 @@ function setupSmoothingFactorTests(options) {
   var smoothingFunc = options.function;
 
   describe(options.suiteName, function() {
-    it('should default to ' + options.default, function(done) {
+    it('should default to ' + options.default, function() {
       (smoothingFunc()).should.equal(options.default);
-      done();
     });
-    it('should throw an exception for invalid values', function(done) {
+    it('should throw an exception for invalid values', function() {
       (function() { smoothingFunc(0); }).should.throw;
       (function() { smoothingFunc(2); }).should.throw;
       (function() { smoothingFunc(-1); }).should.throw;
       (function() { smoothingFunc(1); }).should.not.throw;
-      done();
     });
-    it('should be configurable', function(done) {
+    it('should be configurable', function() {
       (smoothingFunc(0.9)).should.equal(0.9);
       (smoothingFunc(0.1)).should.equal(0.1);
       (smoothingFunc()).should.equal(0.1);
-      done();
     });
   });
 };
diff --git a/toobusy.js b/toobusy.js
index ffff48c..6ded8b6 100644
--- a/toobusy.js
+++ b/toobusy.js
@@ -19,7 +19,7 @@ var SMOOTHING_FACTOR = 1/3;
 // Vars
 //
 
-var lastTime = Date.now();
+var lastTime;
 var highWater = STANDARD_HIGHWATER;
 var interval = STANDARD_INTERVAL;
 var smoothingFactorOnRise = SMOOTHING_FACTOR;
@@ -66,7 +66,7 @@ toobusy.interval = function(newInterval) {
   newInterval = Math.round(newInterval);
   if(newInterval < 16) throw new Error("Interval should be greater than 16ms.");
 
-  toobusy.shutdown();
+  currentLag = 0;
   interval = newInterval;
   start();
   return interval;
@@ -157,10 +157,11 @@ toobusy.smoothingFactorOnFall = function(newFactor) {
 toobusy.shutdown = function(){
   currentLag = 0;
   checkInterval = clearInterval(checkInterval);
+  eventEmitter.removeAllListeners(LAG_EVENT);
 };
 
 toobusy.started = function() {
-  return !!checkInterval;
+  return Boolean(checkInterval != null);
 };
 
 /**
@@ -197,6 +198,9 @@ toobusy.lagFunction = function (lag, cLag, sFactorRise, sFactorFall) {
  * Private - starts checking lag.
  */
 function start() {
+  lastTime = Date.now();
+
+  clearInterval(checkInterval);
   checkInterval = setInterval(function(){
     var now = Date.now();
     var lag = now - lastTime;
diff --git a/yarn.lock b/yarn.lock
new file mode 100644
index 0000000..033ba3c
--- /dev/null
+++ b/yarn.lock
@@ -0,0 +1,343 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+balanced-match@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/balanced-match/-/balanced-match-1.0.0.tgz#89b4d199ab2bee49de164ea02b89ce462d71b767"
+
+brace-expansion@^1.1.7:
+  version "1.1.8"
+  resolved "https://registry.yarnpkg.com/brace-expansion/-/brace-expansion-1.1.8.tgz#c07b211c7c952ec1f8efd51a77ef0d1d3990a292"
+  dependencies:
+    balanced-match "^1.0.0"
+    concat-map "0.0.1"
+
+browser-stdout@1.3.0:
+  version "1.3.0"
+  resolved "https://registry.yarnpkg.com/browser-stdout/-/browser-stdout-1.3.0.tgz#f351d32969d32fa5d7a5567154263d928ae3bd1f"
+
+commander@2.9.0:
+  version "2.9.0"
+  resolved "https://registry.yarnpkg.com/commander/-/commander-2.9.0.tgz#9c99094176e12240cb22d6c5146098400fe0f7d4"
+  dependencies:
+    graceful-readlink ">= 1.0.0"
+
+concat-map@0.0.1:
+  version "0.0.1"
+  resolved "https://registry.yarnpkg.com/concat-map/-/concat-map-0.0.1.tgz#d8a96bd77fd68df7793a73036a3ba0d5405d477b"
+
+concat-stream@^1.4.7:
+  version "1.6.0"
+  resolved "https://registry.yarnpkg.com/concat-stream/-/concat-stream-1.6.0.tgz#0aac662fd52be78964d5532f694784e70110acf7"
+  dependencies:
+    inherits "^2.0.3"
+    readable-stream "^2.2.2"
+    typedarray "^0.0.6"
+
+core-util-is@~1.0.0:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/core-util-is/-/core-util-is-1.0.2.tgz#b5fd54220aa2bc5ab57aab7140c940754503c1a7"
+
+cross-spawn@^5.0.1:
+  version "5.1.0"
+  resolved "https://registry.yarnpkg.com/cross-spawn/-/cross-spawn-5.1.0.tgz#e8bd0efee58fcff6f8f94510a0a554bbfa235449"
+  dependencies:
+    lru-cache "^4.0.1"
+    shebang-command "^1.2.0"
+    which "^1.2.9"
+
+debug@2.6.8:
+  version "2.6.8"
+  resolved "https://registry.yarnpkg.com/debug/-/debug-2.6.8.tgz#e731531ca2ede27d188222427da17821d68ff4fc"
+  dependencies:
+    ms "2.0.0"
+
+diff@3.2.0:
+  version "3.2.0"
+  resolved "https://registry.yarnpkg.com/diff/-/diff-3.2.0.tgz#c9ce393a4b7cbd0b058a725c93df299027868ff9"
+
+escape-string-regexp@1.0.5:
+  version "1.0.5"
+  resolved "https://registry.yarnpkg.com/escape-string-regexp/-/escape-string-regexp-1.0.5.tgz#1b61c0562190a8dff6ae3bb2cf0200ca130b86d4"
+
+fs.realpath@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/fs.realpath/-/fs.realpath-1.0.0.tgz#1504ad2523158caa40db4a2787cb01411994ea4f"
+
+glob@7.1.1:
+  version "7.1.1"
+  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.1.tgz#805211df04faaf1c63a3600306cdf5ade50b2ec8"
+  dependencies:
+    fs.realpath "^1.0.0"
+    inflight "^1.0.4"
+    inherits "2"
+    minimatch "^3.0.2"
+    once "^1.3.0"
+    path-is-absolute "^1.0.0"
+
+"graceful-readlink@>= 1.0.0":
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/graceful-readlink/-/graceful-readlink-1.0.1.tgz#4cafad76bc62f02fa039b2f94e9a3dd3a391a725"
+
+growl@1.9.2:
+  version "1.9.2"
+  resolved "https://registry.yarnpkg.com/growl/-/growl-1.9.2.tgz#0ea7743715db8d8de2c5ede1775e1b45ac85c02f"
+
+has-flag@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/has-flag/-/has-flag-1.0.0.tgz#9d9e793165ce017a00f00418c43f942a7b1d11fa"
+
+inflight@^1.0.4:
+  version "1.0.6"
+  resolved "https://registry.yarnpkg.com/inflight/-/inflight-1.0.6.tgz#49bd6331d7d02d0c09bc910a1075ba8165b56df9"
+  dependencies:
+    once "^1.3.0"
+    wrappy "1"
+
+inherits@2, inherits@^2.0.3, inherits@~2.0.3:
+  version "2.0.3"
+  resolved "https://registry.yarnpkg.com/inherits/-/inherits-2.0.3.tgz#633c2c83e3da42a502f52466022480f4208261de"
+
+isarray@~1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/isarray/-/isarray-1.0.0.tgz#bb935d48582cba168c06834957a54a3e07124f11"
+
+isexe@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/isexe/-/isexe-2.0.0.tgz#e8fbf374dc556ff8947a10dcb0572d633f2cfa10"
+
+json3@3.3.2:
+  version "3.3.2"
+  resolved "https://registry.yarnpkg.com/json3/-/json3-3.3.2.tgz#3c0434743df93e2f5c42aee7b19bcb483575f4e1"
+
+lodash._baseassign@^3.0.0:
+  version "3.2.0"
+  resolved "https://registry.yarnpkg.com/lodash._baseassign/-/lodash._baseassign-3.2.0.tgz#8c38a099500f215ad09e59f1722fd0c52bfe0a4e"
+  dependencies:
+    lodash._basecopy "^3.0.0"
+    lodash.keys "^3.0.0"
+
+lodash._basecopy@^3.0.0:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/lodash._basecopy/-/lodash._basecopy-3.0.1.tgz#8da0e6a876cf344c0ad8a54882111dd3c5c7ca36"
+
+lodash._basecreate@^3.0.0:
+  version "3.0.3"
+  resolved "https://registry.yarnpkg.com/lodash._basecreate/-/lodash._basecreate-3.0.3.tgz#1bc661614daa7fc311b7d03bf16806a0213cf821"
+
+lodash._getnative@^3.0.0:
+  version "3.9.1"
+  resolved "https://registry.yarnpkg.com/lodash._getnative/-/lodash._getnative-3.9.1.tgz#570bc7dede46d61cdcde687d65d3eecbaa3aaff5"
+
+lodash._isiterateecall@^3.0.0:
+  version "3.0.9"
+  resolved "https://registry.yarnpkg.com/lodash._isiterateecall/-/lodash._isiterateecall-3.0.9.tgz#5203ad7ba425fae842460e696db9cf3e6aac057c"
+
+lodash.create@3.1.1:
+  version "3.1.1"
+  resolved "https://registry.yarnpkg.com/lodash.create/-/lodash.create-3.1.1.tgz#d7f2849f0dbda7e04682bb8cd72ab022461debe7"
+  dependencies:
+    lodash._baseassign "^3.0.0"
+    lodash._basecreate "^3.0.0"
+    lodash._isiterateecall "^3.0.0"
+
+lodash.isarguments@^3.0.0:
+  version "3.1.0"
+  resolved "https://registry.yarnpkg.com/lodash.isarguments/-/lodash.isarguments-3.1.0.tgz#2f573d85c6a24289ff00663b491c1d338ff3458a"
+
+lodash.isarray@^3.0.0:
+  version "3.0.4"
+  resolved "https://registry.yarnpkg.com/lodash.isarray/-/lodash.isarray-3.0.4.tgz#79e4eb88c36a8122af86f844aa9bcd851b5fbb55"
+
+lodash.keys@^3.0.0:
+  version "3.1.2"
+  resolved "https://registry.yarnpkg.com/lodash.keys/-/lodash.keys-3.1.2.tgz#4dbc0472b156be50a0b286855d1bd0b0c656098a"
+  dependencies:
+    lodash._getnative "^3.0.0"
+    lodash.isarguments "^3.0.0"
+    lodash.isarray "^3.0.0"
+
+lru-cache@^4.0.1:
+  version "4.1.1"
+  resolved "https://registry.yarnpkg.com/lru-cache/-/lru-cache-4.1.1.tgz#622e32e82488b49279114a4f9ecf45e7cd6bba55"
+  dependencies:
+    pseudomap "^1.0.2"
+    yallist "^2.1.2"
+
+minimatch@^3.0.2:
+  version "3.0.4"
+  resolved "https://registry.yarnpkg.com/minimatch/-/minimatch-3.0.4.tgz#5166e286457f03306064be5497e8dbb0c3d32083"
+  dependencies:
+    brace-expansion "^1.1.7"
+
+minimist@0.0.8:
+  version "0.0.8"
+  resolved "https://registry.yarnpkg.com/minimist/-/minimist-0.0.8.tgz#857fcabfc3397d2625b8228262e86aa7a011b05d"
+
+mkdirp@0.5.1:
+  version "0.5.1"
+  resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.5.1.tgz#30057438eac6cf7f8c4767f38648d6697d75c903"
+  dependencies:
+    minimist "0.0.8"
+
+mocha@^3.5.0:
+  version "3.5.0"
+  resolved "https://registry.yarnpkg.com/mocha/-/mocha-3.5.0.tgz#1328567d2717f997030f8006234bce9b8cd72465"
+  dependencies:
+    browser-stdout "1.3.0"
+    commander "2.9.0"
+    debug "2.6.8"
+    diff "3.2.0"
+    escape-string-regexp "1.0.5"
+    glob "7.1.1"
+    growl "1.9.2"
+    json3 "3.3.2"
+    lodash.create "3.1.1"
+    mkdirp "0.5.1"
+    supports-color "3.1.2"
+
+ms@2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/ms/-/ms-2.0.0.tgz#5608aeadfc00be6c2901df5f9861788de0d597c8"
+
+once@^1.3.0:
+  version "1.4.0"
+  resolved "https://registry.yarnpkg.com/once/-/once-1.4.0.tgz#583b1aa775961d4b113ac17d9c50baef9dd76bd1"
+  dependencies:
+    wrappy "1"
+
+os-shim@^0.1.2:
+  version "0.1.3"
+  resolved "https://registry.yarnpkg.com/os-shim/-/os-shim-0.1.3.tgz#6b62c3791cf7909ea35ed46e17658bb417cb3917"
+
+path-is-absolute@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/path-is-absolute/-/path-is-absolute-1.0.1.tgz#174b9268735534ffbc7ace6bf53a5a9e1b5c5f5f"
+
+pre-commit@^1.0.5:
+  version "1.2.2"
+  resolved "https://registry.yarnpkg.com/pre-commit/-/pre-commit-1.2.2.tgz#dbcee0ee9de7235e57f79c56d7ce94641a69eec6"
+  dependencies:
+    cross-spawn "^5.0.1"
+    spawn-sync "^1.0.15"
+    which "1.2.x"
+
+process-nextick-args@~1.0.6:
+  version "1.0.7"
+  resolved "https://registry.yarnpkg.com/process-nextick-args/-/process-nextick-args-1.0.7.tgz#150e20b756590ad3f91093f25a4f2ad8bff30ba3"
+
+pseudomap@^1.0.2:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/pseudomap/-/pseudomap-1.0.2.tgz#f052a28da70e618917ef0a8ac34c1ae5a68286b3"
+
+readable-stream@^2.2.2:
+  version "2.3.3"
+  resolved "https://registry.yarnpkg.com/readable-stream/-/readable-stream-2.3.3.tgz#368f2512d79f9d46fdfc71349ae7878bbc1eb95c"
+  dependencies:
+    core-util-is "~1.0.0"
+    inherits "~2.0.3"
+    isarray "~1.0.0"
+    process-nextick-args "~1.0.6"
+    safe-buffer "~5.1.1"
+    string_decoder "~1.0.3"
+    util-deprecate "~1.0.1"
+
+safe-buffer@~5.1.0, safe-buffer@~5.1.1:
+  version "5.1.1"
+  resolved "https://registry.yarnpkg.com/safe-buffer/-/safe-buffer-5.1.1.tgz#893312af69b2123def71f57889001671eeb2c853"
+
+shebang-command@^1.2.0:
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/shebang-command/-/shebang-command-1.2.0.tgz#44aac65b695b03398968c39f363fee5deafdf1ea"
+  dependencies:
+    shebang-regex "^1.0.0"
+
+shebang-regex@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/shebang-regex/-/shebang-regex-1.0.0.tgz#da42f49740c0b42db2ca9728571cb190c98efea3"
+
+should-equal@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/should-equal/-/should-equal-2.0.0.tgz#6072cf83047360867e68e98b09d71143d04ee0c3"
+  dependencies:
+    should-type "^1.4.0"
+
+should-format@^3.0.3:
+  version "3.0.3"
+  resolved "https://registry.yarnpkg.com/should-format/-/should-format-3.0.3.tgz#9bfc8f74fa39205c53d38c34d717303e277124f1"
+  dependencies:
+    should-type "^1.3.0"
+    should-type-adaptors "^1.0.1"
+
+should-type-adaptors@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/should-type-adaptors/-/should-type-adaptors-1.0.1.tgz#efe5553cdf68cff66e5c5f51b712dc351c77beaa"
+  dependencies:
+    should-type "^1.3.0"
+    should-util "^1.0.0"
+
+should-type@^1.3.0, should-type@^1.4.0:
+  version "1.4.0"
+  resolved "https://registry.yarnpkg.com/should-type/-/should-type-1.4.0.tgz#0756d8ce846dfd09843a6947719dfa0d4cff5cf3"
+
+should-util@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/should-util/-/should-util-1.0.0.tgz#c98cda374aa6b190df8ba87c9889c2b4db620063"
+
+should@^12.0.0:
+  version "12.0.0"
+  resolved "https://registry.yarnpkg.com/should/-/should-12.0.0.tgz#846667cd241691a6509fff0820f44d39143ddcf7"
+  dependencies:
+    should-equal "^2.0.0"
+    should-format "^3.0.3"
+    should-type "^1.4.0"
+    should-type-adaptors "^1.0.1"
+    should-util "^1.0.0"
+
+spawn-sync@^1.0.15:
+  version "1.0.15"
+  resolved "https://registry.yarnpkg.com/spawn-sync/-/spawn-sync-1.0.15.tgz#b00799557eb7fb0c8376c29d44e8a1ea67e57476"
+  dependencies:
+    concat-stream "^1.4.7"
+    os-shim "^0.1.2"
+
+string_decoder@~1.0.3:
+  version "1.0.3"
+  resolved "https://registry.yarnpkg.com/string_decoder/-/string_decoder-1.0.3.tgz#0fc67d7c141825de94282dd536bec6b9bce860ab"
+  dependencies:
+    safe-buffer "~5.1.0"
+
+supports-color@3.1.2:
+  version "3.1.2"
+  resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-3.1.2.tgz#72a262894d9d408b956ca05ff37b2ed8a6e2a2d5"
+  dependencies:
+    has-flag "^1.0.0"
+
+typedarray@^0.0.6:
+  version "0.0.6"
+  resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
+
+util-deprecate@~1.0.1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/util-deprecate/-/util-deprecate-1.0.2.tgz#450d4dc9fa70de732762fbd2d4a28981419a0ccf"
+
+which@1.2.x:
+  version "1.2.14"
+  resolved "https://registry.yarnpkg.com/which/-/which-1.2.14.tgz#9a87c4378f03e827cecaf1acdf56c736c01c14e5"
+  dependencies:
+    isexe "^2.0.0"
+
+which@^1.2.9:
+  version "1.3.0"
+  resolved "https://registry.yarnpkg.com/which/-/which-1.3.0.tgz#ff04bdfc010ee547d780bec38e1ac1c2777d253a"
+  dependencies:
+    isexe "^2.0.0"
+
+wrappy@1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"
+
+yallist@^2.1.2:
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/yallist/-/yallist-2.1.2.tgz#1c11f9218f076089a47dd512f93c6699a6a81d52"