i have used them before works great

A must have item in a 41-year old plane. Bought extras for friends.

This is a great tool for an easy yet effective way to monitor CO2 in the aircraft cabin.

Every airplane should have a CO monitor in it!

Works as advertised. Confirming a leak and keeping me and my family safe.

Very convenient - no excuse for not having one in the plane.

Simple and super easy. Ive used been using one (replace every 6 months) for several years now. The dot turning dark warned me about an exhaust leak long before it got bad enough to actually smell. Cheap and it works.

I am rating this 3 stars because at 11 months from opening (2/20/2019), holding it in front of my auto exhaust muffler for three minutes produced no darkening - zip. I am buying 3 more and will try the test again with one brand new, hope it clears, and again monthly until I find the sweet spot for replacement. Based on this I would agree the folks who state a six months replacement schedule if it passes the test above.

Adhesive strip on the back is practically useless will not stay attached to the instrument panel.

The glue stickum on the back of this product is useless. It fell off after 5-minutes