Well since we're discussing kill switches here, I'll throw in what I did for a friend some years back who was moving to a big city with a car that was very popular with certain ethnic groups
I installed a momentary pushbutton on the floorboard underneath the carpet, about where the high beam switch used to reside before they moved it to the steering column. This switch had to be depressed while turning the ignition switch in order for the circuit to the starter solenoid to be completed.
This momentary switch was wired to a standard 30A SPDT "ice cube" automotive relay deeply buried underneath the dash that intercepted the start wire from the ignition switch to the starter solenoid.
The wire from the ignition switch went to the 87 (or Normally Open/NO) terminal of the relay and also to one side of the momentary switch. The other side of the momentary switch was connected to the relay coil (either 85 or 86), with the other side of the coil grounded.
The wire to the starter solenoid was connected to the 30 (or COMMON) terminal of the relay.
Now, here's the twist that I have never seen anybody else do: I connected the 87A (or Normally Closed/NC) terminal on the relay to ground using a heavy-gauge wire. What this does is to GROUND the wire going to the starter solenoid when the relay is at rest (or anytime you are not trying to start). So if anybody tries to hot-wire the starter solenoid without first disconnecting the wire to it (and normally you wouldn't because there is normally no need to do so), they are just shorting directly to ground. The potential thief will be confounded by a shower of sparks along with the refusal of the solenoid to operate.
I also installed a hidden "valet/mechanic" bypass switch in parallel with the momentary switch, deeply buried in the dash.
The beauty of this system is, its operation is completely transparent and unobservable to anybody including your passenger - nobody is going to notice your left foot pressing down on the carpet or floormat while you crank the ignition key.
Is it foolproof? No, nothing is, but it DID save my friend's car from being taken (but not from it being torn up inside trying to find that !@#$% relay or switch) on three different occasions. At least with the alarm, there is a chance that it will scare the less-serious scumbags away before they do too much damage. I'm in favor of the IN-CAB audible alarm that is so piercingly loud that one couldn't stand to be in there w/o hearing protection.
You can make this setup from about $20 worth of parts and a few hours of time.