If you’re the type of person who frequently has house guests (we won’t ask why, but we do have our suspicions), take a gander at the August Smart Lock ($199). This new device uses Bluetooth low energy (BLE) along with a smartphone app to automatically lock or unlock your door. It recognizes you as you approach the door and unlocks itself, and you can send an invite to a friend or repairman (or a friend who’s also a repairman) that gives them access to enter during certain times. August co-founders designer Yves Behar and tech entrepreneur Jason Johnson say the lock can be retrofitted to fit over most  deadbolts and installed by anyone in less than ten minutes, plus you can still use your keys at any time.