I don't want to hijack, but about 3 months ago when I found this thread I went on the hunt for a similar device that was currently in production, easy to use, and worked easily. (I'm not saying this product doesn't meet these requirements, just that it is still in testing.)
I've been waiting to do a full write-up, since I wanted to test it, but here is a quick summary.
I ended up with an iSocket ( https://www.isocketsystems.com/en/
). It is made overseas, but got here in a week for $214 including shipping and the addition of a temp sensor. An additional $30 to a company called TruPhone provides me with a GSM SIM Card for the device so it works on AT&T or T-mobiles networks.
Once setup (temp threshold hold, power and notification settings) Just plug it in. You can, among other things, be warned when power is lost, restored, the temp rises or falls above a set point, remotely turn whatever is plugged into it on and off. And, alot more, but that is what I use it for. It has a built in battery so once power is lost it sends you a final text or phone call. There is a companion app. The only caveat is you must have phone service. For me this works, because it is on the same network as my cell phone if either doesn't work, the other won't.
I am currently in the southwest and this has really been a huge peace of mind for our pets.
I will do an official detailed write-up when I return back from my trip. For now if you have questions send me a private message.
Edit - there is also a similar product that works with Verizon, but it requires a subscription. I was not interested in anything subscription based.