The moment I hear an unfamiliar voice, and the beginning of a sales pitch (or anything else I don't want to listen to) I tactfully and confidently speak over them "I am not interested, this is a "do not call" number so please remove it from your list, thank you" and I hang up without waiting for a response.
Yes, it is considered rude to speak over someone when they are talking, but in the long run I'm doing them a favor by not wasting their time talking to someone who is not interested in buying ANYTHING over the phone.
I agree. "Do you have an alarm system" is pretty blatant. But I'll bet they catch some folks with it.