I think the Model 2004 is the best all-around tool, and something I (and we
all in this business) need.  Always on, always reading, reducing the risk
that we'll forget to turn it on and miss finding/confirming a dangerous
situation.

Our pattern is to have it in one of the outside pockets on our toolbag, with
the top front half completely exposed, always on, and then go down to the
basement/utility room, and place the bag down near the furnace/boiler/water
heater area.  Then we proceed around the basement for 20 - 30 minutes,
inspecting the water supply, waste piping, electrical, heat, hot water,
foundation, water seepage/penetration, framing, wood-boring insect presence,
etc., after the hot water has been cranking, and as the heat is cranking.

The 2004 has ALWAYS registered/gone off as I'm visually seeing (and
sometimes when I've missed/haven't yet gotten to) such nasty things as:

- unsealed flue penetrations into the chimney
- very rusted out flue pipes
- flues completely detached from the chimney/exterior vent, expelling
combustion gas freely into the basement air space
- poorly designed flues (e.g. I've seen them look like a 2 - 3 step set of
stairs, and long runs up to 40 ft, some sloped down half a foot from end to
end !!!)
- furnace/boiler/water heater flues for multiple units in 2-4 families
directly opposite each other on a single flue chimney (while one furnace was
off and other(s) on)
- conversions from oil to natural gas with the original oil dampers and
draft hoods still in place on the flues, actually helping to fan the
combustion air back into the basement airspace
- tiny unventilated utility closets with furnace/boiler/hot water heater
completely enclosed, starving for air, and backdrafting significantly as I
cautiously open the door, etc, yuk, etc.

I'm convinced your model 2004 is one of the most effective warning devices
one could have, and I wouldn't even think of not carrying one with me into
an inspection.

Many thanks,

John