System Sensor COSMO-2W

2-Wire Carbon Monoxide and Smoke Detector

Average rating:

(based upon one review)

The System Sensor COSMO2-W is a 2-wire combination carbon monoxide sensor and smoke detector. It requires the use of the System Sensor COSMOD2W Interface module for smoke detection. It will use separate zones for fire and CO detection. Buy the System Sensor COSMO-2W from Alarm Grid.
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The System Sensor COSMO-2W is a 2-wire life-safety sensor that offers CO and fire protection. To use this device properly, you will need a System Sensor COSMOD2W i4 Interface Module. This allows for separate programming to two different zones. A relay and power supervision are both needed.

The module uses photoelectric technology to detect smoke. A built-in 85 dB will ensure that everyone in the vicinity is alerted when the device activates. Convenient LED lights display both smoke and CO status. The device can be ceiling-mounted or wall-mounted, and the necessary hardware is included. The device measures 5.5" in diameter and has a depth of 2.5".

Brand: System Sensor

Difficult to Use
Submitted on 10/17/2019 Alarm Grid

The System Sensor COSMO-2W is a hardwired combination smoke and CO detector. It is a 2-wire device, but it cannot be used with a specified "reset zone" like a 2-wire smoke detector would. Instead, you have to add a separate System Sensor COSMOD2W i4 Interface Module, a reset relay and a CO trigger relay for it to work. This makes the sensor very difficult to program and genuinely more inconvenient than other hardwired life-safety sensor options. The technicians at Alarm Grid do not enjoy working with this sensor, and we do not usually recommend it to our customers. However, it does work well when configured properly, and it is one-go-all-go, which is pretty nice. This device is not easy to work with, which is why we only give it a 2-Star rating.

Having a smoke detector and a carbon monoxide detector in one single device is a novel concept. At first, it may seem like a good idea. It would reduce the number of sensors you need to add to your system. And since this sensor is one-go-all-go, it seems like a winning situation. But really, it is much more hassle than it is worth. Since smoke detectors and CO detectors require different zone settings, you need two (2) separate zones for the device. But since you only have one sensor, it can't wire to two separate zone terminals, at least not on its own. That is where the COSMOD2W i4 Interface Module enters the equation. This module allows the system to understand that one (1) hardwired sensor is being used with (2) different zones. And then you still need the reset relay and the CO trigger relay.

Setting up and programming the COSMO-2W and a COSMOD2W i4 Interface Module is not a pretty process. Most DIY users will not want to take on this challenge. The easiest option if you are wanting to use hardwired smoke and CO detectors is to use a compatible 2-wire smoke at the designated smoke detector zone (e.g. Zone 1 on a VISTA P-Series Panel), and use 4-wire CO detectors at any other hardwired zone. This will require no special equipment, and everything will function beautifully. And you will still be using the same number of zones as you would with a COSMO-2W!

We do not recommend purchasing both a COSMO-2W, a COSMOD2W i4 Interface Module, a reset relay, and a CO trigger relay and trying to set up this configuration from scratch. It is difficult for DIYers. But if you already have this type of set up configured, and you need to add an additional sensor, then buying a COSMO-2W makes sense. No programming will be required, as it will already be completed. Otherwise, using this sensor does not make sense. We give it a 2-Star Rating.

Good: It works well when set up properly; One-Go-All-Go.

Bad: Difficult to set up; Requires separate COSMOD module, reset relay, and CO trigger relay.

Bottom Line: 2 Stars.

System Sensor (the recommend option) doesn't offer a conventional 2-wire CO so the CO1224T is the best option.
Ah - thank you for the help. Last question (hopefully) - is there a conventional 2-wire CO detector that you would recommend? Or just the 4-wire CO detector you listed below?
It looks like even the 4-wire version requires the use of an interface module. You can read the Installation Instructions for the device here: For a conventional 4-wire CO detector, you could try this: The reason the COSMO devices require the interface is that they are both CO and Smoke detectors, so the COSMOD device separates this dual input into it's separate respective zone outputs, one for CO and one for Smoke.
Hi. Trying to stay with a wired CO detector for a Vista 21ip panel. Would you recommend the 4-wire COSMO-4W ( then? Will COSMO-4W interface directly to Vista panel without an interface module?
If you use this device, you would also need this: to act as an interface between the CO detector and the panel. The Vista panels don't currently support a 2-wire CO detector without an interface module. If you only need one CO detector, you might be better off to go wireless, with the 5800CO (
Would you recommend this for a 2-wire carbon monoxide for the Vista-21ip system?
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