Medical device hack attacks may kill, researchers warn (BBC News)

Depends. Running your receiver hardware continuously to see if someone is requesting information often takes much more power than just briefly and occasionally turning your transmitter on and sending a short burst of data. You could periodically power on and poll the receiver instead, but it's still not necessarily better.

For example, a typical low-power RF transmitter chip like the CC1000 (http://www.ti.com/lit/ds/symlink/cc1000.pdf page 7) consumes 7.4 mA in its lowest-sensitivity receive mode, or down to 5.3 mA in its lowest-power transmit mode. Either one can be reduced by turning the transceiver off and on, but you're still better off just using the transmitter occasionally.