Use with a Philips Sonicare smart brush head recognition handle (Philips Sonicare DiamondClean Smart) to unlock. Smart features: Smart mode-pairing triggers your handle to select optimal mode and intensity level for exceptional plaque removal; Smart brush head replacement technology tracks how often and how hard you brush and will notify you when it is time to replace your brush head. Reminder bristles fade to let you know when it's time for replacement. Replace your brush head every 3 months as recommended by the American Dental Association. A fresh brush head every 3 months maximizes the effectiveness of Philips’ unique Sonicare technology.