This is something I’ve really been thinking about after finally buying a bike that would hurt me to lose after so many years of riding cheap bikes. I’m not too worried about serious thieves with bolt cutters and angle grinders, but my wife has a bad habit of leaving the garage door open on accident. It would only take a few seconds for an enterprising neighborhood kid to see the bikes hanging there and ride off with one of the bikes.
The plan I’ve been thinking about is to drill some anchors into the concrete and run a cable through the frames. Obviously this would be easy to defeat with some tools, but I’m not too worried about that where I live.