GPS bike tracking (locks)
Pain in the ass, and waste of money.

As of the last time I checked, you can't track them directly (there'd be no way for you to receive a signal from a battery-operated device 5mi away), so you need to sign up for a recurring monthly service. On top of that, they chew through battery pretty quickly, requiring a recharge every few days.

Contrast that to just buying a decent set of locks. If you need to lock up your bike in the same place every day, get a thick $80 chain and a cable for the front wheel. If you need something lightweight to carry around you, a $50 u-lock is going to be a reasonable level of protection.

If your bike is worth more than a few grand, you're absolutely crazy to leave it outside at all.