Transistor which opens circuit, reverse transistor
Here is a circuit that is on by default and turns off when you apply voltage to the input.



When the input is floating or grounded Q2 is off so R2 works as a pullup resistor that turns Q1 on.

When there is a positive voltage applied to the input then Q2 turns on and sinks current trough R2, that creates a voltage drop across R2 that drops the voltage applied to the base of Q1 and turns it off.

It can also be done with mosfets with a similar logic.