https://9to5mac.com/2016/10/17/apple-store-security-tethers-demo-devices/
“The iPhone will reset when the device is powered off and then plugged in. When removed from the Apple Store, the stolen iPhone can’t do anything but ring for Find My iPhone until the battery dies. The iPhones are also Activation Locked using iCloud as a deterrent just like customer iPhones.”
So yes, they do become bricks...
The phones, iPads and computers can all be tracked.
The stupid Thieves will be caught.