I have
this for low temp and water. It needs a phone line because it calls you when there's an alarm. Instead of paying Verizon for a land line, I got a Verizon Wireless adapter for $20 a month which is basically a cell phone in a box that you plug a phone (or in this case, the monitor) into.
The water alarm does send falsies every once in a while. It's just a set of contacts on a pad that you put on the floor, so dust or a bug can set it off.
I have a guy come and check the place a couple of times a week. Plus I have a neighbor that's an ex-cop.