I use one of the home types from Home Depot. I'm not sure of the brand, but it is one of those with an self contained 8 or so year battery and a digital readout. Never get false alarms. I used to use a very sensitive one designed for aircraft. It worked very very well, and would start with a very little chirp at 10 ppm and then get progressively louder and more annoying as the concentration increased. When a gas boat up wind on the dock would sit and idle, I would know it. I really liked it, but when it expired and I replaced it with the new model, I got so many false alarms that I threw it out.

I would go with the Home Depot one again.