Children, key-stomping cats, hackers, laptop thieves, nosy friends over for a party—these are just some of the entities that make it worth your while to lock your laptop or desktop computer with a password. But typing in that password every time you get up for coffee or other breaks can make you feel like a prisoner of your best planning.
A new iPhone and Mac app combo can make unlocking your main workhorse computer literally as easy as tapping twice. If you work on a Mac and your iPhone never leaves your side, you should consider Knock: free for the Mac part, $3.99 for the iOS app.
Knock uses a Bluetooth low energy to maintain a constant but not particularly battery-draining connection between your phone and computer. Your computer and phone connect whenever they're in range of one another; you tap twice on your phone, and your computer unlocks itself. These type of device-based security schemes have been around for a while: Proximity for Mac, BtProx for Windows, and some intense Linux setups. But with an app that's always listening for a connection, and then listening for two "knocks," it's a good deal easier to balance out security, battery life, and convenience.
Knock is said to work mostly with 2013 and newer Macs and MacBooks, but a writer at The Unofficial Apple Weblog (where I saw this little trick) said their 2012 Mac seemed to work fine, and 2011 MacBook Air or Mac Mini systems should work too. Give it a few knocks and see if a double tap is faster than your password.
Standard writer-not-engineer disclaimer: You shouldn't use Knock with a computer holding sensitive corporate or personal information, as Bluetooth can, most likely, be spoofed and broken by those who really, really want access to your data. Knock is for those looking to balance out the privacy/convenience paradigm.