Vehicle Clinometer / Tilt meter for iPhone, iPod touch, and iPad on the iTunes App Store
And it has a FJ Cruiser built in.

You can set warning/alarm angles, customize colors and device position. Set-up in truck park on level ground hit the cal button and have fun. (if the mount will not be moved you only have to cal once, be sure to turn off auto-zero at startup)
Someone in the comments had a good idea about setting the angles low to scare passengers haha.
I have not gotten it offroad yet but it is fun to play with, only downside I saw is it costs $1.99.
-Boot
And it has a FJ Cruiser built in.

You can set warning/alarm angles, customize colors and device position. Set-up in truck park on level ground hit the cal button and have fun. (if the mount will not be moved you only have to cal once, be sure to turn off auto-zero at startup)
Someone in the comments had a good idea about setting the angles low to scare passengers haha.
I have not gotten it offroad yet but it is fun to play with, only downside I saw is it costs $1.99.
-Boot