Does anyone even pay attention to car alarms anymore? Just sit there and look embarrassed and act like you're trying to make it shut up and 99% of people (1% possibly being a cop) are going to pay absolutely no attention to your alarm.

Once entry is gained, it only takes a few seconds to cut the wires to the siren anyway.

Some kind of axle locks on all 4 would be the only way to keep someone (short of a flat bed) from hauling it off. Never heard of fake towing outfits stealing cars? Happens all the time where chop shops or cars being sent to Russia are concerned. Looks official enough that few mind the car blaring away as it's hauled down the road.

Insurance is really the only way you can protect your investment. Cause it's only a matter of time before something happens to most customized cars. I know, my jeep spent 4 months in the shop after thieves cut every wire under the dash trying to figure out how to get it started. See, with my ignition disabler (my design), you needed power to a relay to engage the start circuit. Most ignition kills need power applied to disable the circuit and the relay is installed directly under the dash (the relay being normally closed). Mine was wired right next to the starter solenoid. In trying to make my jeep start, they cut the wires needed to allow that to happen.

I wouldn't let any old installer do a car alarm. The places that do them like that all use the same routing and locations for given components. Any thief with experience becomes attuned to where to go first to get at the alarm and disable it. Hide the brain, hide the back up battery (an absolute must have) and hide all the wiring for the ignition controls. That way, when the thief looks under the dash, they get puzzled when they don't find what they're expecting to get away with the vehicle. Bury any additional wiring so it's not obvious from underneath that it isn't factory. Anything that looks out of place will just get cut before they attempt entry.

I was pretty involved in custom stereos back in the early 90's (multi-thousand dollar systems). Alarms were a given.