How Do I Wire and Use a COSMO-2W Combination Smoke/CO Detector?

Wire and use the COSMO-2W by connecting the first COSMO-2W to the COSMOD-2W. Wire each additional COSMO-2W in parallel, connecting to the previous device. Connect the COSMOD-2W to the alarm panel using one zone for smoke, and one zone for carbon monoxide. A maintenance zone can also be used.

The purpose of the System Sensor COSMOD-2W is to cause multiple COSMO-2W devices that are connected to it to all sound in sync with one another if any one of these devices initiates an alarm. For this reason, this configuration is really only worthwhile if multiple smoke/CO devices will be in use, particularly over a relatively large area. Because there are now wireless smoke detectors, or combination smoke/CO detectors that support the "One-Go/All-Go" feature, if only a couple of devices will be used, wireless is the route to take when possible.

Because the COSMO-2W combination Smoke/CO detectors are not being connected directly to the alarm panel, a power reset will not occur automatically after an alarm has been triggered. For this reason, a trigger or relay must be used to perform the reset after an alarm. This is much like the one required when 4-wire smokes are used. This FAQ assumes the COSMO-2W and COSMOD-2W are being used with a Vista P-Series Panel, such as the Vista-20P.

COSMOD-2W Terminal Layout:

The diagram below shows the proper wiring, along with some notes on programming. Each numbered item will be further explained below the diagram:

  1. Power Input. One side of the COSMOD-2W power input should be wired through a relay. This relay will provide a power reset after a fire alarm. Either a 4204, 4229, or a low current relay triggered by Output 17 or Output 18 can be used. The trigger can not be used for this by itself, as it does not supply enough current. Regardless of which output is used, the programming will be the same. The relay or trigger will activate on Zone Type. The Zone Type is 54 (Fire Reset) the action will automatically be "Close for 2 seconds" when ZT 54 is selected. The output number will either be the relay which was enabled through Output Device Mapping [*79], or will be either Output 17 (trigger 1) or Output 18 (trigger 2). If a supplementary power supply is used to power any portion of this setup, it must have a common ground with the panel. In this case, DC negative from the power supply should be connected to terminal 4 on the Vista P-Series Panel.
  2. Zone Selection. Any zone other than Zone 1 can be used for the smoke input. When Zone 1 is programmed as a fire zone, the Vista P-Series Panels assume 2-wire smokes are being used, and that the zone will reset automatically after a fire alarm. For this reason, smoke reset logic for the relay or trigger will not kick-in after a fire alarm on Zone 1. Use any other hardwired zone for this.
  3. Bell Resistor. On Vista-15P/20P rev 9 or higher and newer Vista-21iP panels, an 820 Ohm resistor is included for bell supervision. In addition, there is a programming question that allows bell supervision to be enabled or disabled. Even if bell supervision is disabled via programming, the 820 Ohm resistor must be wired in parallel on the bell terminals. This is because supervision voltage is present on the bell terminals, whether the feature is enabled or not. The 820 Ohm resistor will bring this voltage down so that it doesn't interfere with the COSMOD-2W operation.
  4. Dipswitch 1. For the configuration shown, where the bell output is being used to trigger the COSMOD-2W, Dipswitch 1 must be in the ON position. This is the default setting.
  5. End-of-Line Resistors. The panel EOLR must be enabled for the Smoke and CO zones, and they must be connected in parallel on the COSMOD-2W. The panel will supervise the wiring between itself and the COSMOD-2W. The COSMOD-2W will supervise the wiring between itself and the COSMO-2W Smoke/CO units. It comes with its own 3.9K resistor. This FAQ shows how to wire multiple 2-wire smokes in parallel.
  6. CO Trigger Input. A second relay must be used to trigger the COSMOD-2W CO input. This is what tells the COSMOD-2W to sound all detectors in temporal 4 for a Carbon Monoxide alarm. Again, a 4204, 4229, or low-current relay activated by an on-board trigger can be used. The common terminal for this relay will connect to the COSMOD-2W CO Trigger In terminal. Normally Open will connect to a positive power source, such as terminal 5 on the Vista P-Series Panel. The programming will be activated by Alarm on a Zone Number or Zone List (if more than one CO zone is in use on the panel). The Action will be Close and Stay Closed. The programming to stop the relay will be activated by Zone Type, Zone Type 22, and Action 0 - Off, again making sure to point to the correct Relay or Trigger enabled in [*79].

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Hi Matt, thank you for that information. I did find that in the installation instructions after the previous back-and-forth. At first I couldn't imagine a scenario where you'd want to use an i3 smoke with the COSMOD, but I guess it is still useful for reversing polarity and syncing the sounders. Thank you for following up. We, myself in particular, are certainly not infallible, and the more good information we get out there, the better!
The COSMOD2W is compatible with the i3 smoke detector and the i4 series smoke/CO. You simply do not have CO detection on the i3 series. I thought I should clarify so someone in the future is not confused by someone saying they are not compatible.
Howard, I did find a document about a retrofit, using i3 smokes with sounders and incorporating an i4 device into the loop. Are you using the COSMOD2W only to make all devices sound at once if any device trips? Again, it would really be better if you would email us at
Yes it is compatible in COMBINATION with COSMO-2W and 2WTA-B , the System Sensor cut sheet says so and we use them that way all the time. Heat Detectors downstream from the COSMO-2W smokes are not. They must be upstream or on another zone. Do not use the 2w Fire zone (1) for this at all. Yes you can use a 4229 or RBSNTTL to reset.
You're welcome Howard.
Ms Ross ..Thank you very much for your quick response and all your help..
Hi Howard, it may be easier if you send your inquiry into The i3 smokes are not compatible with the COSMOD2W, it's the i4 series smokes that work with it. That's the first potential issue I see. If you plan to use the 4229 relay to do the smoke reset, then it's just a matter of wiring the relay as shown above (using the power supply, rather than the panel terminals, just making sure to have a common negative between the power supply and the panel). The rest is programming, which is fairly easy.
I am trying to install my i3 smokes with the COSMOD2W to my Vista 20P panel using a available Zone on a addressable 4229 Expansion Board. I would like to use my added AL624 Aux Power supply to power the smokes and COSMOD2W if possible . Thanks
The COSMOD2W is not compatible with the 2WTA-B Smoke. Exactly what are you attempting to do? The purpose of the COSMOD2W is allow the combination Smoke and CO wired detectors (the i4 series COSMO-2W in this case) to interface with a wired alarm panel. The COSMOD2W splits the signals, FIRE and CO, into two separate inputs on the panel (the panel has no Zone Type suitable for both FIRE and CO, so it can't be handled by a single wired zone input).
Can you show me how I would wire in the RBSNTTL relay with a Auxiliary Power Supply to the COSMOD2W and 2WT A- B smokes. Can I use a zone on my 4229 expansion for fire? Any additional information would be greatly appreciated..Thanks
How Do I Wire and Use a COSMO-2W Combination Smoke/CO Detector? Great right up ..thanks

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