The present invention concerns a method and a well string element for transmitting data in a well. The well string element (20c) includes an elongated body (80) that defines a through channel (110) and also includes a side pocket (92) that is open to ambient (91); and an acoustic modem (60) provided in the pocket (92) and configured to emit acoustic waves. The acoustic modem (60) is configured to receive electrical signals from one or more sensors (50, 52), transform the electrical signals into the acoustic waves and emit the acoustic waves into a wall (112) of the elongated body (80) when receiving an acoustic wake-up call from a device (70) outside the drill string element (20c).