The 2GIG SMKT3-345 and the Honeywell 5800COMBO are both popular life-safety sensors. They are both used for smoke, heat and freeze detection. But the 5800COMBO provides carbon monoxide detection, while the SMKT3-345 does not. They also differ slightly in terms of system compatibility. Upon initial inspection, these sensors appear very similar. They both provide smoke, heat and freeze detection. They also both operate at a wireless frequency of 345 MHz. Both devices also use photoelectric technology in their smoke detection. Also the low-temperature freeze sensors on both devices will activate shortly after sensing a temperature of 40 degrees Fahrenheit or lower. With all these factors considered, these are actually very similar devices. However, there are some key differences that must be discussed. First is the functionality. The 5800COMBO provides support for carbon monoxide detection. The SMKT3-345 does not have this feature. If a SMKT3-345 user wants to monitor their property for deadly CO gas, they will need to install a separate sensor. The heat detectors for the devices also differ. The SMKT3-345 provides both fixed temperature and rate of rise detection. The sensor will trigger upon sensing a temperature increase of 10 degrees Fahrenheit or higher in a single minute. It will also activate if it senses a temperature of 125 degrees Fahrenheit or higher for three consecutive minutes. But the 5800COMBO only offers fixed temperature detection, and the sensor will activate immediately upon sensing a temperature of 135 degrees Fahrenheit or higher. Finally, these sensors differ in terms of system compatibility. The Honeywell 5800COMBO will work with any Honeywell VISTA (with an added wireless receiver), Honeywell LYNX Touch, Honeywell Lyric Controller, 2GIG GC3 and 2GIG GC2 System. But the 2GIG SMKT3-345 will only work with the 2GIG GC3, 2GIG GC2 and the Honeywell Lyric Controller.