Obviously, the surest way to keep from getting caught in a police speed trap is to not speed. Staying within your vehicle’s limits is also an important part of car safety. But here are five ways to know where speed traps are so you can be sure to keep to the limit.

1. Download Waze

Waze is a navigation app for your phone, similar to Google Maps and Apple Navigation. But what sets Waze apart is that its users contribute lots of helpful data. For example, a Waze users can drop a pin if they see a police speed trap. If you are driving on the same road, your phone will alert you to the potential police officer ahead. Because Waze is a favorite app of rideshare drivers and truckers, it holds a wealth of information.

2. Watch for high beam headlights

You might call flashing your high beams the original version of dropping a Waze pin. In the ancient era, before cellphones, helpful drivers who wanted to warn one another of speed traps needed an analog signal. What they came up with was flashing their high beams at drivers who are headed toward a speed trap.

3. Buy a radar detector

One way many police officers detect speeders is to point a radar gun at oncoming traffic. While you can’t see or hear these radar waves, a purpose-built device can. This radar detector can be as small as a cellphone. It simply suction cups to your windshield or attaches to your dashboard, keeps a look out, and alerts you to any radio waves. Just know that using a radar detector is illegal in Virginia and Washington D.C.

4. Install a police scanner app

Another nifty gadget that may alert you to a speed trap is a police scanner app for your phone. These apps don’t turn you phone into a radio, but they do allow you to play one of many police radio band streaming stations available online. You can pick a station for your local police department and listen in on their chatter. But be careful, this is not always legal. Read more about the laws surrounding police scanner apps.

5. Look for unmarked police cars

In many states, officers can observe traffic from unmarked police cars. In some places, they can even complete traffic stops in unmarked cars. Luckily, unmarked police cars are often easy to spot: many are one of several makes and models and share some common equipment. Find out how to spot unmarked police cars.