Common faults and fixes

  • When inserting a new SIM make sure the power to the unit is off. 
  • Only turn on the unit’s power once the new SIM is inserted.

A red flashing LED on the PCB inside the unit could be either of the following:



There is a possibility that the onboard lithium battery has died. To check, you will need to take a reading of the battery’s voltage. It should be at least 3v DC.

If the readings are under 3v or there is no voltage, then do the following:

For Telguard ML/Optimus products: Simply replace the CR1220 3v battery.

For Telguard HY-CAN products: The board will most likely need to be replaced or returned to us, as the battery is soldered onto a metal partition.



The SMS cache could be full. This is caused by the network provider sending marketing messages to the SIM.

You can clear the cache by doing one of the following:

For units with a keypad:

Type in ‘5787’ followed by the serial number. Once in the menu, key the following sequence:

‘4*’ (wait for a second)

‘8*’ (wait for a second)

‘8*’ (wait for a second)

‘3*’ (wait for a second)

Repeat ‘3*’ to give it an extra clear.

Press ‘*’ 5 times to exit the menu.

For units without a keypad:

If the unit does not have a keypad you can perform the above steps over the phone for any Telguard HY-CAN product.

Call the telephone number of the SIM inside the unit and once the unit has answered, follow the above steps.


If the unit has SWV 1.54 or above, you can do this via text. Send the following text to the unit:


replace ‘serial’ with the 6-digit serial number.

Once you have cleared the cache, you will need to contact your network provider to have all marketing/alert messages switched off to stop this from happening again in the future.

This could be down to a number of things, but here are some checks you can perform before contacting our technical team:

  • If the unit is calling a mobile phone, make sure the receiver of the call has WiFi calling disabled.
  • If the network in the area is down or having issues, this could cause the DTMF tones to stop working. To check if this is the case, try another SIM on a different network in the unit.
  • On landline units, if the line it is connected to has audible interference, the unit may not be able to hear the DTMF tones clearly. If this is the case, you will need to contact the line provider and ask them to perform a test on the line.

Please note: Our systems are experiencing a non-compatibility issue with most digital lines where DTMF tones are not available.

If your customer is using a digital line in their household, it is recommended that they have their mobile phone connected as a point of contact rather than the landline phone which is using the digital line.
Regarding digital line issues, you can refer to the following link:

If the above checks have been done and you are still experiencing issues, please contact our technical team.