A wearable device is used to authenticate a user into a user account at a user device of the user. In particular, the wearable device may include a sensor configured to detect whether the wearable device is worn by or is with the user. If so, the wearable device may send a signal to the user device and the user device may authenticate the user based on the signal received from the wearable device. For example, when the sensor detects that the wearable device is worn by the user, the wearable device may send a unique signal periodically, such as every five seconds or every 10 seconds. Based on whether the unique signal from the wearable device is received, the user device may authenticate the user.