QS1135-840—Resolving a Malfunction
Resolving Errors on a New Device:
If this error occurs on a newly installed device, it is usually an indication that the sensor is too far from the panel to maintain a signal.
Determine whether you are able to move the sensor closer to the panel, or if a signal extender may be your best option.
You can test if this will resolve the issue by bringing the sensor closer to the panel or temporarily moving the panel closer to the sensor, if it is powered by backup battery. Clear the error and see if the issue continues.
Resolving Errors on a Pre-Existing Device:
If the error occurs on a device that has been installed for a long time, it may be that the batteries are too low to maintain a signal.
Learn how to replace the batteries in your door/window sensor here: Replace the Batteries in Your QS1135-840.
As this sensor is most commonly paired with the Qolsys IQ Panel 2, see the following article for information about the error and steps for clearing this error from your panel: How to Fix a Sensor Malfunction on the IQ Panel 2.