In case the battery runs out in remote key

Supposedly there is an NFC (Near-field communication) chip in the remote that allows you to start the car using the method described above. I plan to replace the remote batteries as soon as the dash warning comes on though.

 

You can experiment with it by removing the keyfob battery. Then just hold the keyfob up next to the Power button. As I recall, it's really sensitive to how close you hold it.

One thing you can do with a batteryless keyfob is to leave it inside the car without any shielding (aluminum foil and the like). The car only detects it when you hold it next to the Power button. Then use the mechanical key to lock/unlock the door. The mechanical key (or better yet, a copy of it) can get wet while you go surfing or other water sport, something I don't recommend with the keyfob.

 

^ That's what I do.
I travel 6 counties with my company G3, and I don't want my car to become a 3400# lawn ornament if I fumble the snap and accidently lock the keys in one of my offices.....or the company’s badge system goes tango-uniform...or I just plain lose the keys.
I took the keylet and tie wrapped it to an undisclosed exterior location, and I placed the keyfob (sans battery) in an undisclosed interior location.
Now?
Even if aliens come and transport my duty keys to an undisclosed extra-terrestrial location......I can still get home without waiting for "Larry's Tow Truck Emporium" to come and find me and my immobilized G3.
Yes.
I tested this setup.

Oh....BTW....by aliens I mean real aliens....not undocumented persons who may or may not have been born in the United States (a.k.a. 'illegal') aliens.
Gotta keep PC......er….PC!

 

my wife had to do it in her hycam, it worked just fine.

 

In previous cars, my key batteries lasted about three years so I plan to change the batteries this time on the even anniversaries.

 

This is a documented feature, and the Prius (2010 here) info display will tell you to do this when the battery is low.