Digital clock thermostat for time-dependent monitoring and control of the room temperature, battery version (also for retrofitting with a 2-wire connection), installation on a flush-mounted socket, operation on the device or via app, direct Bluetooth low energy connection (BLE) between the app and the clock thermostat, no communication via the Internet, convenient settings via app with intuitive operation from a smartphone or tablet, increased ease of use, 3 individually programmable weekly programs, as well as comfort, eco and reduction functions, suitable for energy-saving room temperature control in single-family homes, apartments, etc., illuminated display when a button is pressed, external input for the flexible connection of either an external room temperature sensor, floor sensor, motion detector or telephone contact, intelligent control algorithm (pulse duration controller, hysteresis controller), suitable for example. B. for on/off heating, zone or individual room control, electric heating