A device for transmitting data from a movable unit such from a domestic animal contains a conventional passive transponder unit (1) which is coupled to an antenna (3). The transponder (1) comprises means (23) for storing electrical energy comprised in electrical voltage pulses received on the antenna (3) and can by means of the stored energy transmit on the antenna (3) pulse sequences carrying information such as identification data for the device. Further, in the device a permanent electrical current source such as a lithium battery (9) is provided, which powers a processor (7). The processor (7) receives signals from a motion sensor (15) and is coupled to a transmitter (11) having an antenna (13) and can activate the transmitter (11) for transmitting radio signals having a good range, when the motion detector (15) signals an increased activity, such as for a non-milking cow during the estrus period.
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