Circuit for change detection while sleeping

I want to make an XBee device detect a low pulse on an I/O pin that occurs while the XBee may be sleeping. However, since the XBee needs to be awake while the change occurs in order to detect it, most I/O changes will go undetected.

This calls for some external circuitry that records the pulse and is reset by, e.g., the falling edge of the XBee’s ON/SLEEP output. For obvious reasons, this circuit must have low power consumption.

Can anyone point me towards a circuit?

Edit: A J/K flip-flop such as the 74LVC112 seems to suffice, but if anyone happens to know of a clever solution, I’d still like to hear it.