Conventional fire detectors are installed on the ceiling by Fire Regulations. Smoke takes a while to reach the detector by natural convection flow. It could be too late to control it then.
Putting the PDRD device next to the bed, fire smoke close to reach the device and the smoke will be effectively sucked into the device by negative ion air stream moving to the positive grid upward, then it alerts fire earlier than having the detector on the ceiling.
Importantly, the negative ion air air stream purifies smoke and toxic gas, preventing from suffocation.