Need a gas detector for my house (butane / propane)

Very interesting point of view, I completely take it on board and will try and see what I can do to physically restrict the gas. But the trouble is, I am more than capable of forgetting to switch off the main (or even the individual ring if I am honest).

How old is your hob? You might investigate replacing it with a newer version complete with Flame failure (supervision) device - if there is no heat at the burner the hob gas valve will shut automatically.

Wouldn't be very up to date with prices for hobs but must be in the ball park (or cheaper) than the detector, alarm, slamshut valve alternative.

I think your right in having concerns, paranoia is a good thing when it comes to gas, but you have to be practical too, if you fit a alarm you will need a slam shut valve to isolate the gas, these are costly and tend to be troublesome or don't work at all, because of that i wouldn't have one fitted in my house, but having a 2 1/2 year old chef myself who has big eyes for my LPG range cooker, i have a isolation valve fitted in easy reach, i don't always remember to use it, but i do know if i do use it leaves the appliance 100% safe, keeping my paranoia at bay and frustrating my daughter, Gary.