This is the secret that makes the Philips HeartStart FRx AED so 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. It is intended for use on children up to 8 years of age and less than 55 lbs.
 
The key can be used over and over again with no need to replace it. Compare that to the cost of replacing pediatric electrode pads on other AEDs and you'll experience the savings. The HeartStart FRx Smart Pads II are used for all emergencies.