Looking for Smoke and CO2 Sensor Help

[sbex55]

Looks like I'm going to need smokes and CO2 units for an ELK system I'm installing for a friend.  The electrician said we need a smoke in the new construction portion of the house.  So smokes and CO2 sensors are required in the new Master BR and existing LR since the LR is 'on the path' to the new Master BR.
 
I've read the Bosch sensors are good.  I'd like to get a combination unit if possible.  Has anyone used the I4 System Sensor Smoke/Co2 combination unit?  It looks like it uses an 'interface module' which is wired between the combo sensor (via 2 wires) and the panel (via 6 wires).

 

[Del91574]

CO and not CO2? Different beast. Make sure you know which is which and what is required. CO2 would be the first time I heard CO2 detection being required.
 
The I4 detectors work, as do the modules and related components.

Downside is the amount of zones and wiring from the mod to the panel...but it converts a 2 wire fire to a 4 wire type zone, so on some panels you'll have to consider how you're resetting the fire alarm.

 

[sbex55]

CO and not CO2? Different beast. Make sure you know which is which and what is required. CO2 would be the first time I heard CO2 detection being required.
 
The I4 detectors work, as do the modules and related components.

Downside is the amount of zones and wiring from the mod to the panel...but it converts a 2 wire fire to a 4 wire type zone, so on some panels you'll have to consider how you're resetting the fire alarm.

 
Oops ... I guess a sensor for CO2 would be pretty dumb, huh?  Sorry about that.  8)

I'd like to use a single unit for smoke and CO since the homeowner has requested it but I've read enough threads to know that I should avoid 4-wire smokes when possible.  I looked briefly through the I4 SS documentation and assumed they could be wired as 2-wire smokes.  I guess not.  8(

I only have access to one wall in the Living Room and I need to place 2 speakers, the smoke and CO sensors.  Are there any decent 2-wire smoke/co combination sensors?  I am using the Elk M1 panel.

 

[Del91574]

The field wiring is done as a standard 2 wire fire zone. The module converts the 2 wire fire to a 4 wire output as far as the panel is concerned, separate power/circuit. Really not a huge deal. Your field circuit would be a 2 wire fire zone, but at the panel it's wired like a 4 wire circuit as far as the panel is concened.
 
The only item that can't be run on the same 2 wire circuit would be heat detectors.
 
The only combo units on the market that are really available and only require a single pair (or 2 pair, variation) would be the I4's.
 
You can mix/match the I3 and I4 on the same signalling circuit.