Wiring any electrical or electronic project, device or product into a person's house takes a lot of knowledge. You have to know the product is electrically safe, reliable and will not cause any fire-risk.
All the rest of your work is centered around wiring that has been proven to be safe  (except for a Chinese import that fails after a short period of time due to the PVC coating being inferior or made from "regrinds") and you don't want your work to be jeopardized by a cheap alarm failing to meet electrical standards. The main problem is in the plug-pack and it must not get hot or produce any leakage to the secondary side of the circuit.
Only prior knowledge from other electricians can inform you of this. Some plug-packs failed after a few months from a large Australian hobby chain and they were found to contain dry joints and other faults - as advised from the owner of ELECTRON INTERCOMS.
You can get 2-pair, 4-pair and 5-pair twisted telephone cable to run to each of the sensors (keep a record of the colours you have used, so you can trace a fault in a PIR or switch).
Talking Electronics has an ALARM TESTER project to test PIR activation and door switches and you can contact Colin Mitchell for more details.