A wearable device includes: a band configured to at least partially surround a body part of a user； a clasp configured to hold the band in a closed position, wherein the band resists removal from the body part while in the closed position； a lock actuator configured to selectively lock the clasp against moving to an open position； a communication interface configured to receive data from at least one other device； and a processor in communication with the lock actuator and the communication interface, wherein the processor is configured to: receive a locking indication that the wearable device is to be unlocked, and in response to receiving the locking indication, signal the lock actuator to allow the clasp to transition to the open position. The device may further comprise a physiological sensor (e.g. an accelerometer for motion sensing), and an indication to allow unlocking of the clasp may for example be received upon reaching a predefined goal measured by said physiological sensor, e.g. after burning a certain amount of a calories.
