The University of Illinois Medical Center has installed a system called HyGreen (Hand Hygiene Recording and Reminding System) which acts as a reminder to health care workers before they ever enter a patient's room.

The provider begins by cleaning his hands, then placing them under a sensor that recognizes the cleaning, and transmits a signal to a badge the provider is wearing. When they walk into the patient's room, that badge transmits an "all clean" signal to a sensor above the bed.

If a caregiver walks into a room without washing their hands, the sensor won't get that all clean signal and the badge will start buzzing.

References:
Tech Ensures Your Doc Washed Their Hands. NBC Chicago.