Although supposedly calibrated in April, the unit reads anywhere between 2 and 8 ppm in fresh air. If it doesnt settle down soon, I will be calling KWJ Engineering for technical support and may need to exchange it with you.

I have only just started using this, but so far, it appears to work well and has given me a little more information than I had before, such as when idling on the ground, there is a small amount of CO that intrudes into the cockpit (around 4 ppm - not enough to be a health issue), but this level drops to zero in cruise flight. This seems likely to be accurate, as with the exhaust close to the cockpit, some intrusion at idle is likely, but at cruise, the slipstream should keep it all clear of the canopy. I like the functionality of pressing the button once before flight and then having it monitor throughout the flight, but turning itself off 12 hours later to save battery life.

I use this device in my 56 Champ to keep an eye on CO levels in the cockpit, and keep it clipped to the keychain. It responds quickly to changes in CO level, and alerted me to a high-CO condition when I go into cruise descent, that I wouldnt have known about otherwise. The alarm beeper is not loud enough for aircraft use, and I consider it lucky that Ive noticed it beeping when the CO level went over 50 PPM. Ive thought about trying to make a headset mount for it so that beeps and vibrations would be really obvious (plus, that would place it closer to the air Im actually breathing), but that would also limit my ability to see the display, which I usually check multiple times per flight. Overall, Im quite happy with it, and give it 5 stars despite the quiet alarm.

Works as advertised. I bought it since I use a propane heater in my hangar. It has not set off the alarm so far, but my plane tug exhaust did when I was working close to it as it was running. Very satisfied!

This is the second one of these I have purchased for use in my aircraft. I have had the previous one for approximately 5 years and have sent it in to the manufacturer for calibration, but for not much more money I can purchase a new unit, so that is what it did. Unit seems to work well. The only tricky thing is shutting it of manually, which requires you to hit the button 2X but it doesnt always shut it off and puts you into a different mode, otherwise I would give it 5 stars. Unit is preprogrammed to shut off after 12 hours, but that tends to run down the battery. Overall I am pleased with this device.

I like the first one I bought so much that I purchased another for our flying club plane. The detector is easy to operate and very accurate. CO warnings are obvious. I highly recommend Model 300.

Seems well made. Small and lightweight. Havent locked myself in the garage yet with a running car to see if it really works but I think I trust it.

A very useful tool - works well, and well supported by a detailed Instruction Manual. The only problem I have is that the display is small, and not very bold - a little hard to read.

A bit difficult to use and not entirely sure it will save lives. The instruction booklet not very user friendly. Shall consult others in the industry to see if I can work it better.

We have been using two of these units for just over a month now and have been very happy with their performance. Their small size means they can easily be secured by velcro to the aircraft dashboard. So far the monitoring works great and its an excellent safety measure for pilots of our aircraft. Highly recommend for all pilots. Will be carrying one with me whenever I fly!

Too soon to assess durability, but seems to detect CO well from 0-500 ppm with multiple alarm mechanisms (beeper, white backlight, red LED, and vibration) beginning at 50ppm. More features than expected including updated reading every 5 seconds, Total Exposure (concentration x time), 8-hour Time Weighted Exposure, and max CO level. Recommended as one of the least expensive but functional electronic CO detectors.