Which radar detector signal is a cop?

In most of the United States, a Ka-band or Laser/LIDAR alert is most likely a police signal, while K-band can be police or a false source, and X-band is rarely police except in a few regions. In practice, identifying a real cop signal depends on the band, the frequency shown on your detector, how the alert behaves (sudden spike vs. steady), your location, and whether your detector can identify modern photo radar systems.

What the bands mean, and how they relate to police radar

Consumer radar detectors categorize signals by band. Understanding which bands law enforcement actually uses will help you decide when to take an alert seriously.

• Ka band (33.4–36.0 GHz): The dominant police radar band today. Three “hot” centers are common: 33.8 GHz (MPH), 34.7 GHz (Stalker), and 35.5 GHz (Kustom/Decatur). A Ka alert—especially near those frequencies—is very likely a cop.
• K band (24.050–24.250 GHz): Still used by many agencies and by most fixed/mobile photo radar systems. It’s also the band with the most false alerts (door openers, vehicle blind-spot systems), so context matters.
• X band (10.5 GHz range): Rare in 2025, but still in service in parts of New Jersey, Ohio, and a few rural pockets. If you drive there, don’t disable X band.
• Laser/LIDAR (around 904 nm infrared): Not radar, but most detectors alert to it. A laser alert often means your vehicle has already been targeted.

While Ka is the safest “it’s a cop” assumption, K and even X can be real threats depending on where you drive. Consider both the band and the behavior of the alert.

Modern low-power photo radar you may encounter

Many cities use low-power, complex-waveform K-band systems for speed cameras and mobile photo radar. These don’t always look like traditional K-band on older detectors.

• MRCD/MRCT (MultaRadar): Low-power, frequency-modulated continuous-wave (FMCW) K-band typically around 24.080–24.200 GHz. Often used in vans or fixed cameras; requires detectors that specifically support MRCD/MRCT.
• Gatso RT3/RT4: Also FMCW K-band, commonly around 24.190–24.230 GHz, used in fixed and sometimes portable camera systems. Not all detectors can reliably flag Gatso without dedicated support.
• Detector display: Newer models may show “MRCD,” “MRCT,” “Photo,” or a special icon; others may only show a generic K alert with unusual behavior (weak, short, and very directional).

If you regularly drive through camera-enforced areas, ensure your detector firmware includes MRCD/MRCT/Gatso detection; otherwise, you may miss legitimate enforcement on K band.

How to tell a real police alert from a false one

Because many non-police devices emit radar-like signals—especially on K band—use these cues to separate real threats from background noise.

• Band priority: Treat Ka as high priority almost everywhere. Treat K as situational—higher risk in known enforcement zones or where photo radar is used. Treat X as relevant only in the few regions that still use it.
• Frequency readout: On Ka, numbers clustering near 33.8, 34.7, or 35.5 GHz strongly suggest police radar. On K, recurring alerts near 24.1–24.2 GHz can be either police or cameras; exact identification depends on detector capability and location.
• Alert behavior: A sudden, strong “instant-on” burst that appears and vanishes is a classic police tactic. A steady, slowly ramping signal is more typical of fixed sources like door openers or speed signs.
• Location and repeatability: The same K alert at the same spot every day is likely a stationary false (storefront or traffic sensor). A new or moving alert on open highway deserves more attention.
• Directionality and arrows: Detectors with arrows can show whether the signal is ahead, beside, or behind—useful for distinguishing a storefront (side) from a patrol car ahead (front) or behind (rear).
• Visual confirmation: Marked patrol cars, motorcycle units, tripods, vans, or camera boxes near known enforcement areas reinforce that an alert is legitimate.
• Detector filters: If your unit flags MRCD/Gatso specifically, treat those as enforcement. If it labels “POP,” note that true POP is rare; enabling POP detection may increase falses.

No single factor is definitive. Combine band, frequency, behavior, place, and your detector’s features to grade the threat in real time.

Signals that are usually not police

Many everyday technologies share spectrum with police radar, creating false alerts—especially on K band. Knowing the common culprits helps you respond appropriately.

• Vehicle systems: Blind-spot monitoring and adaptive cruise (often around 24 GHz K band, and 77 GHz for some systems) can cause intermittent K-band falses.
• Automatic door openers: Supermarket and gas station doors commonly transmit on K band and create predictable, repeatable alerts.
• Traffic sensors and speed signs: Often constant-on K band; speed signs may be legitimate radar but are not usually used for issuing citations.
• Leaky detectors: Some older or cheap radar detectors emit Ka “leakage,” causing false Ka alerts nearby.
• Industrial equipment: Certain motion sensors and equipment can emit K-band signals that look like radar.

If your detector supports GPS lockouts, you can automatically mute stationary falses after repeated passes—just ensure you don’t accidentally lock out an area that sometimes hosts enforcement.

What your detector can’t warn you about

Not all speed enforcement emits detectable radio or laser energy. These methods won’t trigger your detector.

• VASCAR/time-distance and aircraft enforcement: Officers or aircraft time vehicles over painted lines—no radar involved.
• Pacing: An officer measures your speed by following you at a constant distance.
• Some timing-bar/photo systems: Depending on the setup, they may use pavement sensors or cameras without active radar.
• Laser realities: Even when your detector alerts to laser, it often means your speed was already captured due to laser’s pinpoint beam.

Use situational awareness in addition to a detector; it’s an aid, not a shield.

Practical tips and legal notes

A few setup and policy choices can dramatically improve the usefulness of your detector while keeping you compliant with the law.

• Keep firmware current: Manufacturers frequently update K-band filtering and add MRCD/Gatso support via firmware.
• Enable only what you need: Turn on the bands used in your region. Use Ka narrow/segmentation if your detector supports it and you understand your local Ka usage.
• Tune K-band filtering: Adjust K filters and BSM filters to balance sensitivity and sanity; don’t over-filter if you face K-band enforcement.
• Use GPS features: Lock out stationary falses judiciously; enable low-speed muting for city driving.
• Mount correctly: High on the windshield for radar range; low can slightly improve laser detection but may reduce radar range in hilly terrain.
• Know the law: In the U.S., radar detectors are legal for private passenger vehicles in every state except Virginia and Washington, D.C., and they’re prohibited for commercial vehicles over 10,000 lb under federal rules. They’re also banned on many military bases.
• Drive smart: Detectors are supplementary. Maintain safe speeds and watch for enforcement cues even without alerts.

Set up your detector for your roads and laws, and revisit settings as your routes and local enforcement evolve.

Summary

If your radar detector signals Ka or Laser, assume it’s a cop. K band can be police—especially with photo radar or in departments that still run K—but it’s also the noisiest band for falses. X band is rarely police except in a few regions that still use it. Judge alerts by band, frequency, behavior, and location, keep your detector updated (including MRCD/Gatso support if needed), and remember that some enforcement methods won’t trigger any alert at all.

What alert is a cop car radar detector?

Ka band alerts
It is almost certainly the police. Ka band radar are radar waves between 33.4GHz and 36.0GHz. These are the most recent and the best radar band frequencies that law enforcement can operate on. There are as many as five different frequencies that these waves can operate on.

What radar signal do cops use?

Although the California Highway Patrol uses Ka band exclusively, several thousand K-band radar units remain in service, some of them in California. But if you’re being pestered by K-band false alarms, in your area the risk is low enough to make the move worthwhile.

Is the K band a cop?

Yes, K band is used by police, but it’s not the only source of the signal, so it’s also associated with many false alerts from other sources like automatic doors and blind-spot monitoring systems on vehicles. Ka band is a higher frequency and is more commonly used exclusively by law enforcement, making alerts on this band more likely to be a real police radar signal.
 
How to understand K band alerts

• It’s a common police band: Opens in new tabK band has been used by law enforcement for speed detection since the 1970s and is still in use in many areas. 
• It’s not exclusive to cops: Opens in new tabUnlike Ka band, which is mostly used by police, K band is also used for other purposes, leading to frequent false alerts. 
• Sources of K band signals: Opens in new tabYou can get K band alerts from automatic doors, speed signs, and modern car features like blind-spot monitors and smart cruise control. 
• Use your radar detector’s features: Opens in new tabIf you frequently get K band false alerts, use your radar detector’s filtering or GPS lock-out features to ignore non-police sources of the signal, allowing you to focus on genuine police radar. 

Does a radar detector detect cops?

No, radar detectors do not detect cops themselves, but rather the radar gun or LIDAR gun that the police officer is using to measure speed. A detector will only alert if the officer’s device is actively transmitting a signal. Many officers use “instant-on” mode, turning the radar gun on only when they want to clock a specific vehicle, or they might not have a radar unit on at all, leaving the detector silent.
 
This video explains how radar detectors work and how officers can use “instant-on” mode to avoid them: 59sVortex RadarYouTube · Apr 6, 2018
How Radar Detectors Work

• Detecting Signals, Not Officers: Radar detectors are essentially radios tuned to specific frequencies (bands) used by police radar guns. 
• Transmitting, Not Stationary: The device only signals your detector when the radar gun is actively emitting radio waves, not when it’s in standby or turned off. 
• LIDAR Guns: Some police use LIDAR (laser) guns, which emit a focused beam of light rather than radio waves. Traditional radar detectors cannot detect LIDAR, and because the beam is so narrow, a detector may not alert until it is too late. 

Why a Detector Might Not Alert

• Instant-On (IO) Mode: Officers often use this tactic, activating the radar gun only when a vehicle is close, giving the driver very little warning time. 
• Officer is Not Using Radar: Many police vehicles do not have radar guns, and even when they do, the officer may not be using it for speed enforcement at that moment. 
• Laser (LIDAR) Use: If the officer is using a LIDAR gun, a standard radar detector will not provide an alert. 

What You Can Do

• High-Sensitivity Detectors: A more sensitive detector can provide earlier warning of radar signals. 
• Look for a “Rabbit”: Having another vehicle ahead of you to draw the officer’s radar fire can sometimes alert you to their presence. 
• Awareness of Laws: Check local laws, as using radar detectors is illegal in some areas.