I recently bought new pads and rotors as the ones I had were verily alive however the sensors still hadn't gone off. The new set I bought though doesn't have the sensor (stupid rookie mistake). I know that I can walk into any auto shop and buy a new one for a low cost but is it hard to install it on the new pads or do I even have to buy new ones?

 

The sensor is always bought separately than the pads. Lots of v cheap aftermarket ones which work fine. If the old one didn't go off you can reuse it in theory but the plastic that mounts it into the pad goes very brittle and breaks easily. So more than likely you will break it trying to refit it. So I'd buy a spare

V easy to fit. A bit fiddly to get to the connector up in the wheel arch. There is a diy for brakes on here (called something like 4 wheel brake job XFR) which is a great description. Your brakes may be slightly different sizes and tools but they will be v similar

Only one sensor for front (left wheel) and one for back (right wheel)