The investigators developed the Physical Activity Loyalty Card (PAL) Scheme which integrates a novel physical activity tracking system with web-based monitoring and nudge initiatives. The tracking system used Near-Field Communication (NFC) technology and a "loyalty card" (PAL Card) which contained a passive Radio Frequency Identification (RFID) tag. Sensors were placed along footpaths in the outdoor environment, in the gym and exercise studio, and participants scanned their PAL card at the sensor when doing physical activity (e.g. walking). A transaction (card ID, sensor ID, and timestamp) was recorded and sent via SMS to a secure data centre. Participants logged onto a personal account on the study website (www.palcard.co.uk) and received real-time feedback on various aspects of their physical activity including minutes, distance and calories expended.