Sensors for determining position; Electric sensors; Mechanical sensors; Electrical detectors; Mechanical detectors; Sensors for determining velocity; Sensors for measuring depth; Ultrasonic sensors; Optical fibre sensors; Sensors for measuring speed; On-off sensors; Electro-optical sensors; Optical sensors, in particular connectable to a communications network; Piezoelectric sensors; Remote control apparatus for opening and closing doors; Window and door opening sensors; Sockets, in particular transportable; Humidity sensors; Hygrometers; Temperature sensors, in particular for measuring air quality; Sensors for measuring CO2 concentration in the air, connectable with a smartphone; Detectors and monitoring apparatus for CO2 monitoring, connectable with a smartphone; Pressure sensors; Temperature feedback units; Temperature indicators; Temperature control apparatus; Instruments for temperature control; Heat regulating apparatus; Cameras; Motion-activated cameras; Smoke alarms; Alarm signalling transmitters; Alarm sensors; Alarm signalling receivers; Sound alarms; Alarm systems; Motion sensors; Flowmeters; Surveillance cameras; Video cameras adapted for monitoring purposes; Monitoring instruments; plant sensors; Radar sensors; Portable sensors for measuring body parameters; Portable sensors for measuring vital parameters; Portable sensors for measuring body condition functions; Software applications for applications, portable devices, smartphones, tablets, smartwatches; Downloadable software applications for computers, portable devices, smartphones, tablets, smartwatches; Mobile apps; Software applications for communication with sensors; Detectors and monitoring apparatus for CO2 monitoring that can be activated and deactivated, in particular by means of a smartphone