[Question]: S270 alarm can send SMS messages normally, and can't send SMS messages after changing SIM card.
【Solution】:
   (1) Shut down when changing SIM card;
   (2) After changing the card, please check if the device is in RUN mode and observe whether the signal is registered or not (this section is described on page 9 of the manual);
   (3) If you have already registered the signal, you still can't send a SMS message. Please confirm whether the mobile phone card is in arrears or the SMS function is normal. You can put the SIM card in the mobile phone to test it.
   (4) If the signal cannot be registered, please check whether the module version is the same as the SIM card in the device. The phone card installed in the device is not correct with the module model (2G/3G/4G) of the device. For example: in China, 2G devices do not support telecom cards, 3G devices do not support mobile cards, 4G devices support full Netcom.