Is an RFID key fob less likely to have its signal blocked? Or is it longer range? Or can it be made smaller, or cheaper?

Also, how do infrared devices generate an infrared signal? With an infrared-frequency laser? (I-aser?) I know that microwave lasers (masers) came first, and TV remote controls appeared not too long after that....

  • 1
    \$\begingroup\$ Rf can bounce off wall easier and no aiming needed, also a much greater dynamic range \$\endgroup\$ Jan 7 at 22:53
  • 4
    \$\begingroup\$ Did cars ever use IR? I've never seen it, and it seems like it would be pretty unreliable in sunlight. (there'd be no lasers involved, only LEDs) \$\endgroup\$ Jan 7 at 23:00
  • 1
    \$\begingroup\$ your question appears to be based in part on mis-information ... you are also asking multiple questions that cannot be answered with one answer ... downvoting because of lack of focus \$\endgroup\$
    – jsotola
    Jan 7 at 23:10
  • 1
    \$\begingroup\$ RF works with keys in pocket and has longer range. RF is useful for finding one's car in a carpark even without direct line of sight. Your second question can be answered with a search for "how does aTV remote control work?" \$\endgroup\$
    – Transistor
    Jan 7 at 23:30
  • 1
    \$\begingroup\$ Look up black body radiation the world is so noisy at IR \$\endgroup\$
    – sstobbe
    Jan 8 at 1:20

RF does not require line of sight. Works better in daylight too. It is also harder to crack as it requires more complex hardware than a $5 learning IR remote.

IR devices use IR LEDs, not lasers.

TV remote controls originally used ultrasonic acoustic transmission in 1950s, and switched the ultrasonic transducers to IR LEDs and receivers in the 1970s.


Like Brian Drummond, I'm not aware of car key fobs using IR. A significant change in key fobs is the move from push-button fobs, where the user presses a button sending a burst of RF from the key fob to the car locking or unlocking it, to keyless entry fobs, where the user just stands near the car which unlocks without needing to press a button. Walking away from the car locks it.

This works by the car continually sending out low power (hence short range) RF interrogation pulses to which the key fob responds (also by RF). Unfortunately this design is susceptible to an attack where car thieves uses a receiver and transmitter pair to boost the range of the interrogation pulses allowing the key fob to unlock the car at a greater than normal range e.g. when the key fob is inside a home or other building.

When TV remotes use IR they generate it with IR LEDs, not lasers. IR LEDs work in the same way as any other LED but use semiconductor materials that generate IR rather than visible or UV light. Early TV remotes could use ultrasonic transmitters or even be wired with a long lead running to the TV. Remotes can also use RF. My current TV remote uses Bluetooth.

  • 2
    \$\begingroup\$ Some Mercedes Vehicles in the late 90's used IR where it had to be guaranteed that the driver was in line of sight to the vehicle - e.g. for remote Window-Up. But that is the only application I know of, so definitely not a widespread approach. Sun-blinding of the receiver is of course a problem for IR outdoors. \$\endgroup\$
    – elchambro
    Jan 8 at 1:32

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