iBeacon i6 Ultra-Thin Bluetooth LE 4.0 Programmable Beacon, Square

This was great. Small footprint and easy to setup. The only thing that was bad about it was that one of the tags that I ordered was dead. It had the tab in it and looked like all of the others, except it wouldn't turn on. I put a new battery in and it worked fine. Also, these are very expensive compared to the other iBeacons that I bought. The ONLY thing it had going for it was that it was much thinner, which in my case was pretty important.