I want to build kind of keyless entry for my car.

My car will have a radar sensor and whenever some body approach it, it will trigger a transmitter (unknown)

Then, this signal will wake up a microcontroller(Arduino) on my keychain and it will trigger a classic 433mhz module to send a specific message to the car that will open the car.

The problem here is nothing BUT the transmitter and the receiver while the transmitter can have at much as 10-20mA, because it will only works whenever the radar detect someone close to the car, the receiver(unknown) on the other side must be extremely low current because it will ALWAYS listen and will be powered by a much much smaller battery (compared to the car)

I'm a beginner, i don't know much about electronics. This means i don't know if somethings like this exists..

  • \$\begingroup\$ Are you using any kind of antennas? \$\endgroup\$ Commented Oct 14, 2017 at 0:20
  • \$\begingroup\$ People here really do want to help but you need to put a real question with a question mark. If you haven't already done so check out how we are different from other sites. \$\endgroup\$
    – Bageletas
    Commented Oct 14, 2017 at 5:28
  • \$\begingroup\$ You seem to be trying to re-invent RFID - and they already use proximity keys for cars... \$\endgroup\$ Commented Oct 14, 2017 at 6:40

1 Answer 1


the other side must be extremely low current because it will ALWAYS listen and will be powered by a much much smaller battery (compared to the car)

Wireless remote receivers are available with current consumption as low as 70uA, but this is still much for the typical battery that fits in a keychain remote. Here are a few possible solutions:-

  1. Put the receiver in standby or power down (drawing 1uA or less) and wake up it up with a timer just long enough to check for a valid signal. This could cut the average current consumption to 1% or less, but increases latency to the period of timer.

  2. Use an ultra-low power 'wake-up' rf detector that receives any signals close to the frequency of your transmitter. This would wake up the micro, which then turns on the main receiver to receive the actual signal (if present). To avoid triggering on spurious signals or noise the wake-up receiver should have relatively low sensitivity, but high enough to reliably detect the signal from your car at short range. Here's an example that uses a Schottky diode detector and only draws 400nA:- enter image description here

  3. Use a rechargeable battery that is topped up regularly so it doesn't have to last for more than a few days. Perhaps have a wireless charging station that you hang your keychain on, or some kind of energy harvesting similar to a self-winding watch.

  4. Put a button on the keychain which you press to enable it before use. Alternatively make the button actually unlock the car - then you don't need all the other stuff!


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.