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A passive short-range remote triggered mode of operation for ultra-low power wireless sensor devices is proposed. When a triggering signal or coded sequence is detected, the node is enabled from sleep mode, which it is kept on standby in order to save energy. After a trigger command is received, the node turns on its power-consuming elements. The triggering schemes studied are based on passive circuits that allow ultra-low power operation in standby mode. The trigger detector is made up of two basic elements: a passive tuned filter and an active detector that converts the trigger signal to baseband. The active part of the circuit is a low power comparator that awakens the microcontroller unit of the node when it toggles its output. Two trigger schemes are presented: (a) a low frequency (LF-125 kHz) near field communications (NFC) link and (b) a RF frequency (868 MHz ISM band) link.