Abstract: An air cleaner having a minus ion generator and a positive electrode. The minus ion generator carries a high minus voltage, and the positive electrode carries a high plus voltage. Preferably, the minus ion generator has a heater. The air cleaner may have an absorbing sheet positioned close to the positive electrode. Preferably, the minus ion generator is spaced apart from the positive electrode by a distance not less than a half of the maximum distance between walls of room. Preferably, the high plus voltage is not less than 4,000 Volts, and the absolute value of the high minus voltage is larger than the absolute value of the high plus voltage. Preferably, the air cleaner has a sterilizing function.

Abstract: A crime prevention monitor system which, when detecting an intruder entering into a monitor region, automatically judges quickly and reliably whether or not the intruder is an illegally intruding person on the side of its concentrator center and if so, then issues a highly reliable report to such a restraint organization as a police station. In the system, an image database having image data of authorized persons for the respective monitor regions previously registered therein is provided in the concentrator center so that, when the intruder is present in the monitor region, the image data of the intruder is sampled through a monitor camera and collated with the image data of the authorized persons of the monitor region in question, whereby, when the intruder does not correspond to any of the authorized persons of the associated monitor region, the system determines that the intruder is illegal and reports the presence of the intruder to the restraint organization.