Use a Clifford RSX 3.5 myself. Very useful, the remote gets a lot of attention just kinda wish it had a bit more range. In 'status check' mode, where the receiver checks with the car periodically to get new messages, the batteries do run out in a month or so. However, in the regular 'non-checking' modes, the remote still gets alerts as they happen but the batteries last a bit longer.
Which model were you looking for?