The Philips FRX Infant/Child Key lowers the energy level of the Defibrillation Shock inside the FRX AED instead of through a resistor at the Electrode Pad like most other AEDs do. That is why with other AEDs you have to purchase separate Pediatric Electrode Pads that are more expensive and have to be replaced every 2-4 years. That is what makes the Philips HeartStart FRX AED so cost effective to own. Upgrade from the Philips OnSite AED to the FRX AED with Infant/Child Key and it will actually pay for the additional cost and then some over the life of the AED just in the savings from not having to buy Pediatric Pads every 2-4 years. The key can be used over and over again without ever having to be repalced. The Philips HeartStart FRX SMART Pads II are used for all emergencies both adult and pediatric.