I have a keyless ignition starter for my 2021 Crosstrek PHEV (ie, start/stop button). This is my first car without a physical key ignition starter. I wondered what would happen if the battery to my keyfob were to run out. I asked my dealer and they showed me that I just have to physically touch the start/stop button with the dead keyfob. I asked how is the car able to recognize the keyfob if they keyfob is dead. But, they didn't know. So, I turn to the experts here to answer my burning curiosity!

  • Welcome to Motor Vehicle Maintenance & Repair! Commented Nov 25, 2022 at 21:32

1 Answer 1


These systems use a transponder chip which can be interrogated by the vehicle's security system. The vehicle sends out an RF signal, which energizes the fob's transponder, which in turn transmits the security response back to the car. Just like with a key which has the transponder built into it, it has to be close to the car's security transmitter in order for it to work. When the battery is functioning correctly in the fob, the car and fob can communicate from a distance so doesn't need to be as close.

  • Thank you thank you so much!! This makes the concept super clear to me now. Commented Nov 27, 2022 at 23:00
  • Yep. not much different from your contactless card you pay with or a security tag on items one needs to pay for before going through the scanners on exits at stores...
    – AcePL
    Commented Dec 6, 2022 at 9:15

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