A device to detect the presence of a living being in a motor vehicle includes a carbon dioxide sensor to measure a concentration value representing the carbon dioxide concentration in the motor vehicle, an analysis unit to compare the concentration value or a change value representing the change in the concentration value over time to a threshold, a transmitting device activated when the concentration value or the change value exceeds the threshold and emitting radiated signals by way of an antenna and a receiving device that activates an indicator device when these radiated signals are received by way of an additional antenna.