J.N.
This is a VERY common practice! If it works right, it is a great way to go. First:
**Do some research on the company - who manufactures the system, who monitors, are they licensed, etc.
*Read the contract carefully. Especially how long is it for. We signed a 3 year contract and moved a year later. Now we have to pay for the equipment, move it to our new home, or pay for a system we don't use (they won't even talk about transfering it, thought some might). Make sure that you can also afford payments for the full time of the contract!
*What back-up do they have if electricity/phone lines go down (very important), how do they detect break-ins, and what steps do they take to make sure its you telling them all is ok (there should be a password, even if they dial you, and a panic code if someone is threatening with a weapon).