Bought this one almost three years ago. See they have a newer model now. Worked as advertised, one time the door was left open and another time the coils froze over in ice. Great peace of mind for $16.00.
I bought this one last week. Haven't had a chance to mess with it yet though.
Update on this. I just set the device up and set my alarms. It will text and/or email you when an alarm condition happens. Of course if there's a power outage it wouldn't work.
Anyway, I like it and set up was easy. Had some trouble with the app but the company walked me through my problems. Looks good so far.