Be Lucent Prism Sonic Electronic Toothbrush is featured in Wired. Check out the article https://www.wired.com/gallery/best-electric-toothbrushes/.

Or read the review below:

This one auto-starts. The Prism sonic toothbrush took one feature from manual brushing that other brands haven't figured out: Just put it in your mouth and brush to start the vibrations automatically. No button pressing needed. It cleans well, too, and the back of the head has the best tongue cleaner of any brush I've tried. It's rough enough to really scrub.

Don't worry, there is a button for controlling the modes or manually turning it on and off. It took me a few times to stop the automatic gesture of pushing it I'd developed from years without an automatic brush. The charging dock is also fun. It reminds me of an ’80s glass block wall, and I mean that as a compliment. (I want to build one of these in my house.)