Step 1: Materials and Tools.
-chain- 10' for $9.98 from Lowes
-18 gauge steel galvanized wire (wire from a coat hanger might work as well) - had this from previous projects, but $4.88 from Lowes
-PVC tee- $1.87 from Lowes
-tube insulation (for pipes?)- OPTIONAL $4.98 from Lowes
-padlock- had it from a school locker, but from Lowes I see one at $2.98
-black electrical and duct tapes or tape of your choice- had them in the tool chest (I assume you might as well...handyman's secret weapon and all)
-pliers with wire cutting capability
-Dremel tool with cutting disc or bolt cutters- OPTIONAL
Grand total: $24.69
Obviously, you could get all of this from someplace other than Lowes and probably for cheaper (especially if you recycle). You just never know what you might find on the curb or the free listings on Craigslist. Seriously, you'd think people's pianos and treadmills were possessed or something....but I digress.
Step 2: Making the trunk loop.
Step 3: The chain and padlock
Voila! You now have a bike-to-car lock. Good luck and happy biking!
Note: Try this all at your own risk. You can't hold me responsible if something bad happens. As with anything, if a thief REALLY wants to steal your bike or your carrier, this lock isn't going to stop them. With the right tools, they can still get through. Consider this fair warning. Regardless, this lock should stop your average grab and go hooligan.