No need alarm la.

Just install a few IP cameras. For a terrace house, I used 6 units of TP-Link Tapo. Cheap and good. As for wiring, I used PVC casing with strong double sided tape.

Quoted how much? If got budget can consider Ajax wireless. And if considering CCTV never go for TPlink, it sucks. Better stick with big brand like Dahu/HIK/UNV

I agree with this.

For alarm, just install a magnetic triggered siren for every door/window which intruder deemed able to access.

The rest is just IP cameras. TP-Link or Xiaomi ones are good. But make sure your router has ample processing power.

Don't bother with HDD recorder type CCTV. Every burglar already knew to disconnect & take it away.

Hacking in old house without knowing the history and layout of piping.. well there are cases where the pipe run in odd places so you will run that risk of hitting something. Due to the nature of brickwall and concrete it is not so straightforward to detect using stud finder unlike all the youtube video made by angmoh as their house made of wood frame/drywall.

That is the risk you have to take if die die want to hack everywhere. There could be better idea like running it behind the floor skirting or;

for horizontal runs use colour-matching wires vs wall colour (since alarm/POE cables are usually thin) and glue it to the corner between ceiling and wall.. if done correctly you also won't really notice it.
for vertical runs from ceiling downwards (limited hacking) just do it as its lower risk.

Actually the whole problem is not whether "got such thing as mini trunking?".
In Bolehland.. apa pun tak ada one.. not the first time.. my dad has been complaining about this "got money want to buy also cannot find" problem.
There are very few sellers carrying mini trunking commonly (meaning cheap like 2-3 bucks a meter, not RS component/element14 specialty store pricing) because conduit used for 230V cables the smallest common size is that 3/4in (20mm wide) one. Can fit in 6 power cables only.

If the alarm is only using the small DC low voltage wires (like telekom copper landline) then it should be very easy to somewhat camouflage-install on the surface without bothering with conduit hacking.

Can you spot my fiber cable? No PVC casing.
Yeah all the wifi equipment and house phone are on top of bookshelf for better coverage; and also hardly use the landline so accessibility doesn't matter