Bluetooth receiver as an on/off switch
You are looking for Bluetooth 4.0 I think. Lower BT versions are not made for energy efficient systems. Notice you probably want to stay connected to the BT device because:


Polling/inquiring is were BT normally wastes more power.
You may want to have "real time" response (you don't want to wait until the BT devices are synchronized). Going from standby to connected status may take from more than half a second (known address) to several seconds (unknown address) which is definitively a non real time response.


There are also low power modes for the BT (park, hold and sniff), which you can use to quickly change to the active (connected) status for data transmission.

Sorry for the mixed up ideas in the response, it is better if you read a little bit about BT versions and architecture if you are interested. Otherwise my advise is, again, go for BT version 4.