The sensors are behind the intake manifold which is behind the plastic air intake manifold between the cylinder heads. The intake manifold is bolted to studs in the heads, it might be possible to remove the intake from the heads but it would take custom tools to do it. Its easier to remove the heads with the intake manifold still attached. If you get on a step ladder and shine a light down from the top of the engine behind the intake manifold you can see the wires going down to oil pressure sensors, there's two. there is also a temp sensor, and knock sensor back there.
The alarms momentarily sound when the key is turned to run as a test. If the alarms go off with engine running and the oil pressure light stays green all is fine.
