This BetaLock carabiner, by outdoor goods company Matador, can be locked with a TSA-compliant key.
It weighs just 55g (1.94 oz) and has small deadbolt.
Being made of aluminum, it won’t stand up to a bolt cutter, but it’s lighter than carrying a padlock around and is simply meant to deter casual theft.
It can also be paired with the BetaLock accessory cable for looping around larger objects. The 24″ cable is made of braided stainless steel coated in TPU, and comes with a little silicone gizmo to store it in.
The carabiner runs $30, and the cable is $10.
Source: core77