K- Carbon monoxide is produced as a result of incomplete combustion. That means that when gas, or any other fuel is burning CO is given off together with CO2 and other substances. If you're dealing with electrical products only and have no source of flames you don't have to worry about CO.
I don't see how your air conditioner can be a source of CO, but if your water heater is gas powered, it may be giving off CO if the burners and exhaust system are not working properly.
Carbon monoxide poisoning can have really severe consequences. Its odorless, colorless and if you have any reason to suspect that you and your family are being exposed to CO I strongly suggest to get a CO detector, and make sure that you find the source and fix it.
You can find CO detectors in most hardware stores, or could buy one onine. Be sure to place it relatively close to your source of combustion and make sure to place it low to the ground, as CO is heavier than air and will settle in the bottom first. If you have it too high, you are potentially not going to get an alarm until the gas reaches that level.
Having a CO detector and explosive gas detector (most units do both things together) can be a life saver at home. Even if you don't have an immediate threat or a potential source of your own, I recommend every household to have these detectors.
Good luck, and let me know if you have anymore questions.
Itay.