I've never heard of a CO2 alarm - though do have a CO alarm nearby as the cylinder is near the gas boiler. It is though in the garage which is well ventilated, and we don't exactly spend lots of time in it so I'm comfortable that it's a low risk. I'm going to leave things as they are, I've sprayed the leak detect all over the joints, valves, dials, tubing, manifolds and regulators and not a bubble to be seen, so I'm just going to leave be for now. I'll see how I get on next time I'm carbonating something.I don’t believe you should be concerned by that leakage rate, as others said - calculate the pipe volume and do the maths. You’ll be putting more out yourself.
However, it’s still a potential hazard if something goes wrong. Weakest link and all. Gas cylinder valves aren’t really designed to be turned on and off frequently.
You might consider a CO2 alarm.