Sensi is an internal anti-chop technology featured in the IR3 (actually, COPS and the more adjustable, intuitive COPS II were featured on the IR3, but the hard technology is the same), Speed and A4 Angel models. It basically places a piezo electric strip contained in a plastic box underneath the breach, with a rod resting on the strip and protruding into the bottom of the breach. When a ball falls onto the rod, the rod depresses the strip and generates an electrical signal which the board interprets as a "ball ready" signal. If a ball isn't detected, Sensi reduces the marker's ROF to allow time for another ball to fall. It never really caught on due to COPS and COPS II requiring some setup in the IR3, and nobody ever bothered to read the manual and properly taylor it to their loader. In the Speed and A4, Sensi, a self-adjusting version of COPS was introduced, but because of the reputation of it's predecessor it never caught on, and WDP ultimately started using the infrared break beams from the Fly up. Despite it's bad rap, I very much like Sensi. In my experience it's been a very effective anti chop system, and because it's all contained internally, it doesn't detract from the good looks and clean lines of the marker.