TheStack's speed programme is a closed loop: the app prescribes a weight and decides when to progress you based on numbers it did not collect, which means the system does not work until something is measuring your swing. This is that something. The Stack Radar reads swing and ball speed without ball contact, estimates carry and smash factor, and pairs to TheStack app over Bluetooth so each set's number lands where the prescription is built. It will also work as a standalone speed readout on the range or in a net. The reason to know it exists is arithmetic rather than technology: quoted next to a fixed-protocol speed trainer, TheStack looks like a modest premium, and it stops looking modest once you add a device to it. If you already own a launch monitor that reads a swing with no ball, you do not need this. If you do not, this is the cheapest honest route into TheStack, and the total is the number to compare against the alternatives.