diff --git a/build/actions/os.js b/build/actions/os.js
index 1a4373d9..91a2645b 100644
--- a/build/actions/os.js
+++ b/build/actions/os.js
@@ -1,5 +1,5 @@
 (function() {
-  var _, async, commandOptions, elevate, mkdirp, npm, os, packageJSON, path, resin, updateActions, visuals;
+  var _, async, commandOptions, elevate, mkdirp, npm, os, packageJSON, path, resin, umount, updateActions, visuals;
 
   _ = require('lodash-contrib');
 
@@ -15,6 +15,8 @@
 
   visuals = require('resin-cli-visuals');
 
+  umount = require('umount').umount;
+
   commandOptions = require('./command-options');
 
   npm = require('../npm');
@@ -97,7 +99,7 @@
   exports.install = {
     signature: 'os install <image> [device]',
     description: 'write an operating system image to a device',
-    help: 'Use this command to write an operating system image to a device.\n\nNote that this command requires admin privileges.\n\nIf `device` is omitted, you will be prompted to select a device interactively.\n\nNotice this command asks for confirmation interactively.\nYou can avoid this by passing the `--yes` boolean option.\n\nYou can quiet the progress bar by passing the `--quiet` boolean option.\n\nYou may have to unmount the device before attempting this operation.\n\nSee the `drives` command to get a list of all connected devices to your machine and their respective ids.\n\nIn Mac OS X:\n\n	$ sudo diskutil unmountDisk /dev/xxx\n\nIn GNU/Linux:\n\n	$ sudo umount /dev/xxx\n\nExamples:\n\n	$ resin os install rpi.iso /dev/disk2',
+    help: 'Use this command to write an operating system image to a device.\n\nNote that this command requires admin privileges.\n\nIf `device` is omitted, you will be prompted to select a device interactively.\n\nNotice this command asks for confirmation interactively.\nYou can avoid this by passing the `--yes` boolean option.\n\nYou can quiet the progress bar by passing the `--quiet` boolean option.\n\nExamples:\n\n	$ resin os install rpi.iso /dev/disk2',
     options: [commandOptions.yes],
     permission: 'user',
     action: function(params, options, done) {
@@ -131,10 +133,12 @@
           message = "This will completely erase " + params.device + ". Are you sure you want to continue?";
           return visuals.patterns.confirm(options.yes, message, callback);
         }, function(confirmed, callback) {
-          var bar;
           if (!confirmed) {
             return done();
           }
+          return umount(params.device, _.unary(callback));
+        }, function(callback) {
+          var bar;
           bar = new visuals.widgets.Progress('Writing Device OS');
           params.progress = _.bind(bar.update, bar);
           return bundle.write(params, callback);
diff --git a/doc/cli.markdown b/doc/cli.markdown
index a12479f6..17d789cb 100644
--- a/doc/cli.markdown
+++ b/doc/cli.markdown
@@ -675,18 +675,6 @@ You can avoid this by passing the `--yes` boolean option.
 
 You can quiet the progress bar by passing the `--quiet` boolean option.
 
-You may have to unmount the device before attempting this operation.
-
-See the `drives` command to get a list of all connected devices to your machine and their respective ids.
-
-In Mac OS X:
-
-	$ sudo diskutil unmountDisk /dev/xxx
-
-In GNU/Linux:
-
-	$ sudo umount /dev/xxx
-
 Examples:
 
 	$ resin os install rpi.iso /dev/disk2
diff --git a/lib/actions/os.coffee b/lib/actions/os.coffee
index d3e5050a..b6e00f7c 100644
--- a/lib/actions/os.coffee
+++ b/lib/actions/os.coffee
@@ -5,6 +5,7 @@ path = require('path')
 mkdirp = require('mkdirp')
 resin = require('resin-sdk')
 visuals = require('resin-cli-visuals')
+umount = require('umount').umount
 commandOptions = require('./command-options')
 npm = require('../npm')
 packageJSON = require('../../package.json')
@@ -108,18 +109,6 @@ exports.install =
 
 		You can quiet the progress bar by passing the `--quiet` boolean option.
 
-		You may have to unmount the device before attempting this operation.
-
-		See the `drives` command to get a list of all connected devices to your machine and their respective ids.
-
-		In Mac OS X:
-
-			$ sudo diskutil unmountDisk /dev/xxx
-
-		In GNU/Linux:
-
-			$ sudo umount /dev/xxx
-
 		Examples:
 
 			$ resin os install rpi.iso /dev/disk2
@@ -168,7 +157,9 @@ exports.install =
 
 			(confirmed, callback) ->
 				return done() if not confirmed
+				umount(params.device, _.unary(callback))
 
+			(callback) ->
 				bar = new visuals.widgets.Progress('Writing Device OS')
 				params.progress = _.bind(bar.update, bar)
 				bundle.write(params, callback)
diff --git a/package.json b/package.json
index 16bd67ca..0da703a2 100644
--- a/package.json
+++ b/package.json
@@ -67,6 +67,7 @@
     "resin-settings-client": "^1.0.0",
     "resin-vcs": "^1.2.0",
     "tmp": "^0.0.25",
+    "umount": "^1.0.0",
     "underscore.string": "~2.4.0",
     "update-notifier": "^0.3.1"
   }