Since Jan 1 of 2011 it's been required that homes have carbon monoxide detectors. Do you have one installed yet?

CO has no smell or color so it's impossible to know it's there, but it's very dangerous. 

SB 183
(eff. Jan. 1, 2011)
This law enacts the Carbon Monoxide Poisoning Prevention Act of 2010.  The law requires a carbon monoxide device (battery or hard-wired) to be installed in a "dwelling unit intended for human occupancy."  A violation is punishable by a maximum fine of $200 for each offense.  Owners of residential rental property must also comply with this law.  Tenants are responsible to notify the owner of an inoperable or deficient carbon monoxide device.
Installation Time Period:

• On or before July 1, 2011 for existing single-family dwelling units
• On or before Jan. 1, 2013 for all other existing dwelling units

Required or not, the detectors are cheap and easy to install so there's no reason not to. Combined smoke/CO detectors are a simple, quick solution.