Bianca Key

About

https://biancakey.com is a smart tracker using built-in https://www.thetileapp.com/en-us/ technology. For the same price as Tile (a little less while they're in pre-orders) you'll get a tracker that's actually built around an uncut house key. After getting it cut at a local hardware store, you can use it with your existing locks. Seems like a great plan for places with lots of roommates.