Problem with CO/LP Detector

I purchased an LP leak detector since this morning and no leaks were found with the detector either so I'm leaning toward a bad monitor. My black tank is almost empty and was not emptied around the time this happened, I don't have a dog and my voltage is right where it should be since I'm on shore power and not using the furnace.

I think I'm going to replace the monitor as bad as I hate to due to the price. I do have another CO only monitor that is still working so I will just turn the LP off at night until the new monitor arrives.