Neat post from a guy who breaks out a load of standard hobby digital electronics tools to reverse engineer his alarm system. In the process, he discoveres a number of serious problems, like the fact that the reed switches on doors don’t transmit unless the switch gets tripped… or that a replay attack on the system ought to be trivial.
In other words, not only can you bypass the system entirely with a crude jammer, but you can do all the alarm stacking you want with a decent transmitter and antenna. Were someone dumb enough to deploy this over a larger area, you could have all kinds of fun.
Too much to quote.