will outside alarm void warranty?

I'm buying a RAV 4 and the dealer says I should be careful about having someone other than the dealership install the alarm because I could void the warranty. I know they have to prove the work done by an outside installer was the cause of a failure before they void the warranty, but I'm a bit wary now. I know it would be less expensive with an outside installer, and probably better than the dealer's alarm (or so I've been told). Any advice?
Thanx!:frown: