Well I was suggesting really any kind of quality electronic alarm system.
You can wire in sirens, shock sensors, motion sensors, door sensors, hood sensor, glass break sensors, starter disconnects, backup batteries, remote door locks, remote windows, remote start, text, wireless paging. The list goes on and on depending upon how much money you want to spend.
Viper is a brand which I believe to be fairly high quality. I have one in my one of my other classic cars.
I had exactly the problem worried about. My wife went into the grocery store for 15 minutes, parked our '89 Blazer. Came back out and the only thing in the parking lot was a small pile of glass.
Police actually recovered the vehicle about 2 weeks later. However it had been completely raped. They had smashed the vent window, from there it's a simple matter to actuate the power door lock switch. Boom they're in.
As noted the steering column lock was destroyed and off they went.
At the time I had an under dash kill switch however it wasn't being utilized. Not sure it would have helped because I do believe the thieves are smart enough to look for these under the dash.
There's another kind of kill switch system that can be purchased that utilizes one, two, or three switches.
And it's impossible for a thief to understand what position all three switches must be in, and in what order they must be turned on, to enable engine start. I was thinking about investigating that. I'll see if I can find a link for it.
VIPER is the most recognized name in vehicle security and auto remote start systems, and an industry leader in cloud connected car technology. VIPER products include car alarms, remote car starters, wireless home security and automation, window film, window tint, SmartStart, interface modules...
www.viper.com