Hiding a spare electronic key in the Prius Prime...

I hide my spare keys with zip ties, they don't fall off.

Try ACE HARDWARE for a spare key.

 

Wrap your spare key in aluminum foil to block the radio. That will keep the car from sensing it.

I traded up a prius for a newer prius at the dealer, and I did not want to forget the second key because of how much it would have cost me.
Putting the second key in the car was problematic. Wrapping the key in foil worked.

jp

 

Do be sure to test this before depending on it. When my fob battery was dying, and I wasn't replacing it immediately due to an extended trip, it took several tries to get the starting procedure done correctly. From memory (I don't have the manual at hand now), it seems it required pressing the brake first to wake up the RFID detection, then holding the fob to the power button. But read the manual, don't rely on my fading memory.

 

Assuming Gen 4 Hatchback is similar to Prime in this regard, I just took my de-activated fob into the cabin and pressed the Power button without the brake pedal. The screen said, "Key not detected". I then moved my fob near the power button and it was recognized and the display lighted up to the accessory power display without pressing the brake pedal or touching the power button again.

 

This sounds like some improvement added since my Gen3 was built.

 

Don't wrap a fob in aluminum foil and then leave it there for 5+ years. The battery will die and corrode all over the electronics. Best to remove it, and then the aluminum foil isn't necessary anyway.