When an alarm is fitted by a proper alarm co. they do boring stuff called commissioning
All the circuit readings are taken at the control panel, then all the resistance, voltage and current reading are recorded to add fault finding.
Fast forward 17 years later & when the tamper circuit plays up , you'd measure the circuit to find rather than 28.5Ω its now measures 380Ω
Each device measures under 3Ω apart from the kitchen pir measures over 300Ω, removing the tamper wires & twisting together the circuit now read 3Ω, pir tamper switch is knackered replace item.
Do you have a fat wife who waddles across the landing squashing the alarm wire between the floor board & central heating pipes ? - rewire & book her into slimming world.
Do you have mice eating the cables in the loft or under the floor ? - rewire & get a cat
Is the front door on the alarm on the global tamper ? its probally corroded on the terminals... replace it
Its basic fault finding, normally I'd not wire anything new doubled poled & the aux tamper would be most likley used for a speaker...