A radar detector is an electronic device used by motorists to detect if their speed is being monitored by police or law enforcement using a radar gun. Most radar detectors are used so the driver can reduce the car's speed before being ticketed for speeding. In general sense, only emitting technologies, like doppler RADAR, or LIDAR can be detected. Visual speed estimating techniques, like ANPR or VASCAR can not be detected in daytime, but technically vulnerable to detection at night, when IR spotlight is used. There are no reports that piezo sensors can be detected. LIDAR devices require an optical-band sensor, although many modern detectors include LIDAR sensors. Most of today's radar detectors detect signals across a variety of wavelength bands: usually X, K, and K_a. In Europe the K_u band is common as well. The past success of radar detectors was based on the fact that radio-wave beams can not be narrow-enough, so the detector usually senses stray and scattered radiation, giving the driver time to slow down. Based on a focused laser-beam, LIDAR technology does not suffer this shortcoming; however it requires precise aiming. Modern police radars incorporate formidable computing power, producing a minimum number of ultra-short pulses, reusing wide beams for multi-target measurement, which renders most detectors useless. But, mobile Internet allows GPS navigation devices to map police radar locations in real-time. These devices are also often called "radar detectors", while not necessary carrying an RF sensor.