How to use PC mic to trigger android google
If the headset is connected to the computer only, then this can't be done solely via Tasker. You could have a computer program that listens on the headset and sends some type of trigger (SMS, PushBullet, etc.) or an entire command to your phone. Tasker could then detect this trigger and open voice command (though it would be listening via the phone mic) or, if the program sent the entire command, Tasker could then be used to process this command.