How about install a hkc alarm , stick a wireless contact any old how and follow the zone inside on a sounder , and have app alert you aswell , must be a way ....
What about hot wiring an wireless door bell from Argos , the door bell switch might be able to be operated like that somehow
Otherwise you will have to an on a tx Rx somewhere and spend loads on a chime
Ps does the Optex AX-100TFR cost more than the takex?
Maybe this version isn't correct for your application so explain application and then perhaps go for another model?
Although you can get small low voltage buzzers
Out of curiosity ,it has a relay output
I assume your having it on your drive and using it as an alert or something? So it's cabled back to the house?
If so then you can use any PSU with extra relay and any chime
But what do you mean it only has a 3.6v output?
It's possible , especially with DIY stuff and depend on position of sensors and other factors batteries , what heating controls you have , some are worse than others
Point behind intruder company
Allot of them actually only have basic experience in fire , as the fire companies have basic experience in intruder
Few smaller companies hold expertise in both when a problem occurs
Or they just to busy to give it real attention, small contract not being worth much