Our Cessna 172P is equipped with a digital CO-meter rather than the traditional Quantum eye carbon monoxide detector. Today I was flying along in winter conditions, and naturally used cabin heat. During the flight, I heard some occasional short beeps, and couldn't figure out what it was. I looked at the CO-meter which has a red alarm light, but that light was definitely off. On the ground, after shutting down the engine, I heard another short beep, and it definitely came from the CO-meter! The digital readout was showing 10ppm. During post-flight, with the door open, the readout dropped to 0 ppm. I routinely check the CO-meter battery during preflight, so I'm pretty sure the beep is not a reminder for a dead battery.
According to these sources: http://www.coheadquarters.com/ZerotoMillion1.htm , http://library.thinkquest.org/10121/textonly/exposure.htm and wikipedia 10ppm is nothing to be concerned about with exposure over a two-hour flight.
Does anyone else have a digital CO-meter and can tell if a reading of 10ppm is normal with cabin heat? Or should I be concerned our exhaust or heat exchanger is faulty?