CO Alarm

Yes it is that simple, just make sure you include a diode with that output, so that there is no back flow to the arduino.
Yes, there will be some back flow, because you are powering an induction coil and that can easily go back to the arduino if there is no protection.

Refer to this:
http://www.google.com/imgres?imgurl=http://www.rc-float-flying.rchomepage.com/Schieppati/relay.jpg&imgrefurl=http://www.rc-float-flying.rchomepage.com/Schieppati/switch.html&h=575&w=614&sz=61&tbnid=kHyZ81Sdu5HngM:&tbnh=90&tbnw=96&zoom=1&usg=___cJ8v52BkbNEl4q2jzvrmcH1C4Q=&docid=RG2MIHS9qpcXZM&hl=en&sa=X&ei=4FWlULWtHKTE0QGk_YGoCw&ved=0CEMQ9QEwAg&dur=0

WOW, that is a long one, sorry about that.