Replacement Unit - Wireless Room Thermostat for CM927 CMS927 CMS927B1049 Honeywell 7-day programmable room thermostat to replace existing Honeywell CM series wireless thermostats. Uses 868MHz 'Ramses 2' RF protocol. This thermostat is nearly identical to Honeywell Home's T3 Series Thermostats (with the exception of not having the +1 function and no flame icon when there is heating demand. The user display otherwise is identical). It will bind directly to an existing Honeywell BDR91 Wireless Relay Box (these are square not rectangular, see note below), whereas the T3 series won't. This means you do not need to get an installer out to fit a new thermostat.