Tell me one thing...what's worse, replacing a jammed lock or replacing a broken window because the idiot who wants your gear just busted it out with his screwdriver.
No alarm or lock cover is gonna stop someone if they really want your gear. You're better off buying a policy specific to your gear (check with insurance company) with no deductible...and specify any damage done as a result of a break in is deductible free as well. From what I've been told, coverage for stereo gear should be about $1/month for every $1000 in gear. Also, specify you want agreed value coverage. Otherwise, you spent $1000 bucks on that new deck/amp/whatever, and it gets jacked tomorrow, they can pay you $150 bucks and call it even. When you go to get your coverage, MAKE SURE YOU HAVE RECEIPTS, even if theyre just handwritten ones from your buddy selling you his used set of tweeters. MAKE SURE THAT YOU HAVE THE VALUE, THE DATE, AND SIGNATURES FROM YOU AND YOUR BUDDY ON THERE.
HTH,
Eric