I found a manual here:
http://www.safehomeproducts.com/shp2...als/70-742.pdf
But to tell you the truth it doesn't immediately suggest a solution. I would look at the pattern of the beeps and the what the lights are doing and see if that suggests anything to you.
Once you have the pattern of the lights and the beeping down I would call the manufacturer.
Check the battery voltage with a volt meter. My detector acts strange if battery voltage is low. Other than that it's well-behaved.
On one occasion it went strange on me. Just kept howling for no reason. I had to cut the wire in the back to get it to shut up. I let it sit for an hour or so and then hooked it back up. No problems since. If you can find a way to cut power to it that might perform a full reset of the device.
I also have a second CO detector that I keep in the sleeping area. It has a digital readout of the CO level. It would be good to check with two detectors. It doesn't sound like there is actually a CO problem but if there is then it's a bad thing.
Propane levels you can cross-check with your nose.