Incoherent.
You don't say where the fingerprint sensor is.
Either way, you probably need to configure the smart device as a slave. I understand this is possible but I have never heard of anybody actually doing it. Once done, you can configure an HC-05 Bluetooth on Arduino as a master with power-on auto-connect. I assume the fingerprint sensor is on Arduino. In that event, "power-on" is the aforementioned control of Bluetooth via mosfet as a response to the fingerprint sensor.
The point of all this is far from clear, and I suspect you just need to get over your paranoia and simply have one or the other programme controlled by fingerprint and not worry about controlling Bluetooth.
I also suspect you need to get wise about the difference between pairing and connecting. This whole deal is probably simpler than you think.