transponder

American  

[tran-spon-der] / trænˈspɒn dər /

Or transpondor

noun

1. a radio, radar, or sonar transceiver that automatically transmits a signal upon reception of a designated incoming signal.

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transponder British  

/ trænˈspɒndə /

noun

1. a type of radio or radar transmitter-receiver that transmits signals automatically when it receives predetermined signals

2. the receiver and transmitter in a communications or broadcast satellite, relaying received signals back to earth

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transponder Scientific  

/ trăn-spŏn′dər /

1. A radio or radar transmitter and receiver that responds to an incoming signal either by broadcasting its own predetermined signal (as in aircraft identification systems) or by relaying the incoming signal at a different frequency (as in satellite communications).

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Etymology

Origin of transponder

First recorded in 1940–45; trans(mitter) + (res)ponder

Example Sentences

Tracking site MarineTraffic said the Karachi transited the strait with its automatic transponder system activated -- where most vessels keep it turned off to avoid being targeted.

From Barron's • Mar. 17, 2026

These efforts could, for example, make the International Maritime Organization’s transponder system truly universal, with important collateral health and safety benefits.

From The Wall Street Journal • Feb. 18, 2026

They said the plane was broadcasting its military number through the transponder, but the boat targeted in the strike likely lacked the equipment to read the radio signal identifying the plane.

From Salon • Jan. 13, 2026

He said that in order to fly in civilian airspace, the military helicopter would have needed to be fitted with a transponder alerting surrounding aircraft to its position.

From BBC • Jan. 30, 2025

The null-gee doughnut that our apartment was spoked into had a supply of escape-jumpers, single-use jet-packs with a simple transponder that screamed for help on all the emergency channels.

From A Place so Foreign by Doctorow, Cory