This thesis compares several technologies to detect human vital signs in cars, in particular respiration and heartbeat, to avoid babies from being left behind in the car. The thesis starts with imposing mandatory and trade-off requirements. The thesis continues with a global overview of the possible technologies based on a literature study. The most promising technologies for our implementation: radar, sonar, infrared and optical camera are chosen to investigate further. Based on this further investigation, the technologies are compared based on the mandatory and trade-off requirements.