General question, just wondering with a view to buying

On bigger set ups ie commercial you can have a solenoid valve but I’m domestic set ups if you have a recent certificate all should be good and keep it up each year. You would smell a gas leak instantly and can turn gas off and call a gas safe registered engineer. Hope this helps

A Carbon Monoxide Detector is a must have for any fossil fuel appliance, although It's strongly advised to have an annual service carried out on your appliances to ensure correct and safe operation. Relying soley on Carbon Monoxide detectors to keep you safe is a mistake because you are relying on it "going off" before YOU do. As for gas leak detectors, no there is no such thing for the domestic market. If you have your gas appliances serviced each year, then you should request that a "tightness test" is carried out. Please be aware that the gas safety installation and use regulations do not currently require a tightness test to be carried out on an annual service, so if you want to be sure that it will be carried out, then you will have to explicitly request for this as many companies will not do this as standard, but we always do as a matter of course.

You can get a gas angel gas sniffer and separate carbon monoxide and smoke detector. Gas angel are the ones the fire brigade fits for free in some areas.