Other ways to trigger head unit other than rear reverse light?

[Sacit]

I recently installed an Android head unit in my 2013 automatic Mazda2. I am looking for alternative ways to trigger my head unit other than rear reverse light bulb possibly somewhere from near the dashboard.

Any suggestions? Thanks!

 

[Nd4SpdSe]

Trigger what, the reverse camera when it's not in actual reverse?

 

[Sacit]

Trigger what, the reverse camera when it's not in actual reverse?

I figured it out. I tapped into back up light in the back.