Setting parse-numbers: false caused number options to become strings as well. Since we seem to have little control over positional arguments, let's make it an option instead.

lib/cli/device/index.js

@@ -1,4 +1,4 @@
-module.exports.command = 'device <serial>'
+module.exports.command = 'device'
 
 module.exports.builder = function(yargs) {
   return yargs
@@ -101,6 +101,11 @@ module.exports.builder = function(yargs) {
     , type: 'string'
     , default: 'ws://${publicIp}:${publicPort}'
     })
+    .option('serial', {
+      describe: 'The USB serial number of the device.'
+    , type: 'string'
+    , demand: true
+    })
     .option('storage-url', {
       alias: 'r'
     , describe: 'The URL to the storage unit.'