Meet the Davek Alert Umbrella: a smart umbrella with a Bluetooth-based proximity chip in its handle that pairs with your phone and lets you know when you are about to leave it behind. The umbrella looks sleek and works with iOS and Android devices. The battery life should last you up to 2 years.
The companion app lets you set up your umbrella, turn off alerts, and even check the weather forecast. You can find this smart umbrella on Kickstarter.