An apparatus includes a strap configured to enable the apparatus to be worn by a user； an optical measurement element configured to be placed on a skin of the user, and to measure data related to heart activity of the user； communication circuitry configured to transmit the data related to heart activity of the user according to a Bluetooth standard on a 2.4 GHz band； and an antenna coupled with the communication circuitry, and configured to access a radio interface to transmit the data related to heart activity of the user.
