This key makes the Philips HeartStart FRx AED cost effective to own. Other AEDs use pediatric electrode pads for use on children. It means you'll have to regularly replace them just like adult electrodes pads.
The FRx uses a "key" that when inserted into the device, converts the FRx into a pediatric defibrillator.
The key can be used over and over again with no need to replace it.