Found on the Spanish (Mx) User’s Guide, pages 21 and 22:
Your device may have an internal antenna and an external one. As with all other radiotransmission devices, avoid unnecesary contact with the antenna’s area while transmitting or receiving information (signal). Touching the antenna affects quality of the communication and may cause the device requires more energy than necessary to operate, which reduces battery life.
The figure shows the antenna area marked in gray
pages 8 and 9