I have been getting an 'Accessory Tamper' message (and alarm!) on the control panel our Friedland Response SA6 alarm for a few days now. The control panel log does not inform you what is causing this, just that it is happening.
In this case it was caused by a micro-switch inside the door sensor battery lid. The switch, which is normally held closed by the lid, was reading a varying resistance when measured with a digital voltmeter on the 0-200 ohm setting, whilst held down. It shouldn't do this!
A drop of WD40 onto the switch (which is small, perfectly square, and has a circular operating button) was worked into the switch innards by pressing it a number of times. Afterwards, the resistance dropped to near 0 ohms, as it should be when pressed.
The alarm has not shown this message again in the last 10 days (was as often as every few minutes before.) I have put a drop of WD40 onto the switches on all the other door sensors as an insurance - I think this is due to some slight corrosion or dirt inside the micro-switch, the WD40 helps remove this.
Don't forget to put the alarm into 'walk test' mode before you do this procedure, this will replace the alarm siren with a simple 'bing-bong' door chime when you remove the door switch covers (i.e. 'tamper' with them), at least until your revert to 'normal' mode. How to set this 'walk test' mode is in the Friedland owners manual.
HTH