Meet Bar Sensei: an iOS compatible smart gadget that connects to your Olympic bar to give you feedback on your lifts. It connects to your smartphone via Bluetooth, allowing you to see lifts and trends as you improve. The device weighs only 1 ounce and is compact enough not to get in your way.
The sensor provides you with feedback on power, force, speed, and bar distance. Premium apps are available for it too. The above video shows what you get.[Source]