A sad type of incident, which predominantly happens in warm and sunny seasons, is children dying of hyperthermia inside vehicles. In the US, there are, on average, 37 heat-related fatalities per year. In about 70% of these cases, the child was either forgotten or intentionally left inside the vehicle. Temperatures rise very quickly in a car that is parked in the sun, and can reach a critical level within less than 20 minutes. Although the overall number of hyperthermia fatalities can seem relatively low compared to the overall road fatalities, the incidents are dramatic, as the victims are predominantly very young and defenseless. A sensor, integrated behind the headliner of the vehicle, uses radiofrequency (RF) signals to detect the vital signs of a child. The sensing unit emits signals in the 24 GHz ISM band and evaluates the reflected signal. The system is sensitive enough to detect the small breathing movements of a sleeping baby, and is even capable of detecting the child under difficult circumstances, such as through the sunshade of a rearward-facing child seat. Once the presence of a living being is detected, various alerts or countermeasures can be initiated. A vehicle-based sensing approach is the most promising, as it can potentially use all of the vehicle’s available infrastructure to initiate warnings or countermeasures. Further studies on warning strategies may be needed to identify the most effective and acceptable ones.