Meet the Swing-OPS Speedsensor: a baseball swing measurement system that helps you measure your bat speed and swing power. The display on the device shows your speed after each swing. The device connects to your iPhone via Bluetooth. In standalone mode, it can record and store up to 50 swings.
The Speedsensor can be attached to any bat. The companion app lets you analyze and compare your swings. Like what you see? You can get one for under $100.