Meet the Pillar: a smart lockbox that you can control with your smartphone and voice. It connects to your iOS/Android device and works with Kensington cable locks. This lockbox has a rechargeable battery that lasts up to 6 hours. It also has a fail-safe master password just in case.
The Pillar measures 4″ in diameter. It stands 6″ tall. Costs under $110 at this time.