Believe it or not, my cordless phone sets off my alarm. We made this discovery by accident one day when we happen to make the connection that every time my mom took the handset past my car to get to the backyard, my alarm would wail. Before identifying the reason, we always used to yell at my mom for touching my car. I've got sensors up the yingyang hidden in my car and always blamed it on over sensative sensors. Never did we think that a cordless phone would be the cause.
The likelyhood of you having the same problem is slim. I just thought I'd just share my little story and maybe, just maybe you have the same problem. You prolly have a loose connection somewhere or a faulty brain...alarm brain specifically
BTW-I love my mom and did apologize for falsly accusing her of touching my car