There is a fantastic water leak/flood detector https://www.pumpalarm.com/ which is ideal if you're in an area that has Verizon cellular coverage (even if it's a fringe area with only one bar signal strength). It will warn of water, high and low temperature alerts, and loss of power using a text message.

If you have Internet (normally) there is also the La Crosse Alerts 926-25104-WGB Wireless Monitor System Set with Water Leak Probe http://www.amazon.com/Crosse-Alerts-926-25104-WGB-Wireless-Monitor/dp/B00BTJQTTM/ref=sr_1_3?ie=UTF8&qid=1423491865&sr=8-3&keywords=la+crosse+alerts

The PumpAlarm costs $30/year for the text service account and is much higher quality (with excellent support) than the La Crosse system (which is $11.88/year per sensor and has the worst support response time I've ever experienced... took several weeks for them to get back to me). Pumpalarm will continue to communicate freeze/water conditions even if power is out, and will report almost immediately when power goes out and comes back on. La Crosse Alerts will report that it's offline after 30 minutes, and report when it's back online, but you'll not have any info about freeze/water while it's offline.