They adjust automatically, hence auto leveling. When you turn on the car at night and if you have your low beams on, you will see the lights swivel left and right as they adjust themselves. You can also see the headlights aim up and down on its own when you have passengers get in or out of your car. For example, when someone gets into your backseat, you will see the lights dip down a bit and when they get out it'll raise back up. It also adjusts itself when you're stopped on a slight incline/decline.

 

It's done via a sensor mounted on one arm at the rear axle. It measures the suspension compression. More load on the back the higher the aim so the sensor send s a signal to the HID motors to compensate and lower the beam.

In Canada we get manual leveling LOL first time I've seen it on a HID equipped car so you get a switch numbered from 1 to 5 you get to chose like the old days on halogen lights in Europe. (Only tech pack has everything auto leveling, adaptive light steering angle dependent and high beam control for all the lazy people that forget to turn their high beam off of when meeting with oncoming traffic)

Here is a picture of the sensor that measures the pitch of the car. The pic is from a different car if i remember correctly Mazda has it on the left side.

 

I also have a CX-5 Grand Touring with the tech package, everytime i turn the car on i can see the LED lights auto leveling on the Wall in front of me, but with the 3, which uses bi-xenon HID bulbs, the lights stay idle, i can't see the lights autoleveling, i don't have the adaptive lighting package on the 3 but the car manual states that the car has the auto-leveling equipped. Weird.

 

If you see this button on the left under the dash than you have manual leveling and they do not check the limits (reset) by going up and down (and/or left right with AFS I suppose, on an older BMW it did that, not too sure about Mazda, I'm missing the feature :| )

 

Do you have the sTouring or sGT? On the mz3 only the sGT gets auto leveling adaptive headlights.

 

AFter Reading @mateiux response i took my investigation further and found that the lights only level whenever the car is going up or down on a slope, but don't auto adjust on start up like my CX-5.

yes i do have the sGT

 

Go up and down with the electric seat LMFAO. I've never heard that one before.

 

i think the common misconception is that the car levels the headlights based on incline. the car adjusts it's headlights AUTOMATICALLY based on the amount of people in the car. similar to the older MANUAL headlight leveling, you adjust it from 1 to 3 depending on how many passengers you have.