Take a look at Cerberus [1], it has a lot of very helpful features that I haven't seen on other similar apps. Eg take silent photos on incorrect login attempts and email them to you, disable power-off, survive factory reset. I used it once successfully to recover my lost phone. It automatically sent photos to me of the person who found it, and I made my phone speak out a voice message asking them to please stay there while I came to collect it. The guy who found it was looking stunned when I arrived there a few minutes later.

I'm not affiliated with Cerberus in any way, just a happy customer.

[1] https://play.google.com/store/apps/details?id=com.lsdroid.ce...