Combination detectors are smoke detectors that also measure carbon monoxide. This combination of a carbon monoxide detector and a smoke detector provides extra safety. You also no longer need a separate smoke detector or carbon monoxide detector in the room where you hang it. For example, you place combination detectors near the boiler. This way, you get a carbon monoxide warning in time, but you also notice it when a fire breaks out. There are basic combi detectors and smart combi detectors with a smartphone app, so you'll receive notifications from the device on your smartphone.