Automobiles feature many hydraulic pressure switches, although this is true of any piece of equipment or vehicle that relies on hydraulic fluids, including aerospace devices and many other motorized vehicles. The applications are as simple as activating a braking light after detecting a rise in pressure of brake pipes. In airplanes, these signals can be very important to the pilot, as he or she needs to constantly monitor hydraulic fluids that operate plane flaps, lights, landing gear, and various types of coolant throughout the craft. Rocket propulsion operates on directional pressure release, so these types of switches are very important in launching satellites and spacecraft. These situations are much more volatile than a simple braking light activation, as improper pressure monitoring can result in explosions.