As wife said, we have had SimpliSafe for three years. Wired it directly to the 12 Volts, via DROK Buck Voltage Reducer Converter 12V to 7.5V 3A/22W Step-down Power Module DC/DC Voltage, and put base station behind bedroom TV, where it was easy to tape 12 Volts.
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
I have solar on the roof, so I don't worry about batteries being drained, but that might be something to think about if leaving in storage for a long time without some kind of trickle charge.
Since I have Lithium batteries, I also have a Temperature sensor in the battery box, which I can check current temperature with my phone or computer. If it hits freezing, an alarm will be sent to me and dispatch.
Cameras require WiFi. If you want record what they see, it is an extra $5 per camera (which we don't do that). Live view is included in $24.95 plan, not sure about the $14.95 plan. We have a Cradle Point router with Modem Cap, so we have WiFi wherever there is a Cell tower.
PM me if you have any questions.