Pressure Plate Track

This is the switch you use when the thing crossing the wire is a minecart rather than a player on foot. An ordinary plate under a rail does nothing when you roll over it, so any automation along a line, doors opening ahead of you, lights coming on, a booster firing, has to sit on one of these.

Speed breaks it. Push a cart past roughly 95 mph and the trigger can be skipped entirely, which is easy to hit on a long straight run with the faster carts. If a door keeps failing to open in time, brake earlier rather than rewiring the circuit.

They also generate as part of natural trap setups, so a stretch of track you did not lay is a warning rather than a convenience. Dangersense lights them up, which is the cheap way to spot one before you ride into whatever it is wired to.