This guide will cover the horn, headlight, and emergency signal laws in California.

Horn, Headlights, and Emergency Signals

Use Your Horn

Only when necessary, to avoid collisions.
To try to get “eye contact” with other drivers. You may tap your horn to alert another driver who might turn in front of you and cause a collision.
On narrow mountain roads, where you cannot see at least 200 feet ahead of your vehicle.

Don’t Use Your Horn

If a driver or bicyclist is going slowly, and you want him or her to drive faster or get out of your way. The driver or bicyclist may not be able to safely go faster, due to illness, being lost, intoxication, or having mechanical problems with the vehicle.
To alert other drivers that they made a mistake. Your honking may cause them to make more mistakes or to become angry and retaliate.
Because you may be angry or upset.
To honk at pedestrians, bicyclists, or motorcyclists unless necessary to avoid a collision. Remember that your horn sounds much louder outside a vehicle.

NOTE: Honking your horn may startle other drivers. It is safer to slow down or stop instead of honking your horn.

Use Your Headlights

When it is cloudy, raining, snowing, or foggy. If weather conditions require you to use your windshield wipers, you must turn on your low-beam headlights — it’s the law.
On frosty mornings, when other drivers’ windows may be icy or “fogged.”
Any time conditions (clouds, rain, snow, dust, smoke, fog, etc.) prevent you from seeing other vehicles. Other drivers may have trouble seeing you, too.
On small country or mountain roads, even on sunny days. This helps other drivers see you and may help you avoid a head-on crash.
When necessary to get another driver’s attention.

Use Your Emergency Signals

If you can see a collision ahead, warn the drivers behind you by turning on your emergency flashers or tapping your brake pedal quickly three or four times. You can also use the hand signal when slowing and stopping.

Never stop on the road, unless necessary for safety or to obey a law. If you need to stop, then start braking early as a signal to the cars behind you. If your vehicle breaks down on the road, make sure that other drivers can see it. If you experience vehicle trouble, and need to stop, follow these rules:

Pull off the road away from all traffic, if possible.
If you cannot get completely off the road, stop where people can see you and your vehicle from behind. Do not stop just over a hill or just around a curve.
Turn on your emergency flashers if you are not moving. If your vehicle doesn’t have emergency flashers, turn signals may be used instead.
If it is safe, lift the hood to signal an emergency.
Give other drivers plenty of warning. Place emergency flares or triangles 200–300 feet behind the vehicle. This allows other drivers time to change lanes, if necessary. Be very careful when using flares. They may cause fires, especially when used near flammable liquids.
If you do not have emergency flares, follow the rules listed above and stay in your vehicle until help arrives. Be careful for your safety and stay off the road.
Remember: Do not try to change a tire if it means you have to stand in a traffic lane.

Text Messaging and Cell Phones

It is illegal to drive a motor vehicle while using an electronic wireless communication device to write, send, or read text messages, instant messages, and e-mailsunless you are 18 years of age or older and using an electronic wireless communications device designed and configured to allow voice-operated and hands-free operation to dictate, send, or listen to text-based communications when operating a vehicle.

Although hands-free devices are permitted (except for minors), drivers should minimize distractions to focus on safe driving practices.

Call for help in emergencies only.
If your cell phone rings, do not answer it. Let the call go to voicemail if you have this feature.
If you must make a call, pull safely off the road and stop before making the call.
Keep telephone conversations short or if possible, have a passenger make the call.

Do not use your cell phone: