What we typically do when bikepacking/touring is to take the OttoLock that Matthew recommended. It’s quite light and it’s not all that easy to defeat. To that, we have recently added the Knog Scout which is a combination of an alarm and an Apple “Find Me” device. You can set it so that if your bike is jostled, an alarm goes off. That makes your bike a much bigger hassle to deal with than someone else’s. When combined with the OttoLock, I think it’s a pretty effective combination.

The other big advantage to the Knog Scout is that you can pretty well be certain that your bike has made it on the plane or if it hasn’t (which has happened to us) you know where it is when you have to deal with the airlines baggage people. You can usually see it as it moves through the baggage handling as long as any of the people on the ramp have an iPhone. It behaves, in that application, just like an Apple AirTag. We mounted ours beneath the bottle cage.

Knog Scout: https://us.knog.com/products/scout
OttoLock Hexband: https://www.ottodesignworks.com/shop/p/hexband