Real-world Feedback and Control Systems

What are four examples of feedback/control systems you encounter in your everyday environment?

1. Swipe access doors
Sensor- A sensor reads the magnetic strip on a OneCard.
Control mechanism- If the sensor determines that the code written on the magnetic strip has access, a signal is sent to the actuator to unlock the door. Otherwise, no signal is sent.
Actuator- The mechanism that provides the energy to unlock the door. (A motor?)
What works well: The door only opens if it reads a card with access, so other people can't get in. The door doesn't stay unlocked for very long. This way, people without access can't sneak in after you.
What Doesn't Work Well: Sometimes the reader doesn't read the card and you have to swipe more slowly or swipe twice.

2. Handicap doors 
Sensor- The button on the wall near the door is the sensor.
Control mechanism- When the button is pushed, a signal is sent to unlock the door.
Actuator- The mechanism that provides the energy to unlock the door. (A motor?)
What works well: Very effective. I've never seen a door fail to open when the button is pushed.
What Doesn't Work Well: People use it just because they're lazy and therefore waste energy. The door stays open for a long time, so people who don't have access can get inside.

3. Ionization smoke detectors
The battery in the smoke detector sends voltage to plates, making one positive and one negative. A radioactive isotope in the detector decays at a constant rate and emits alpha particles.  They ionize with the air flowing through the chamber in order to create a constant current between the two plates. When the air flowing through the chamber has particles or water vapor in it, it can interrupt the current.
Sensor-The sensor measures the current flowing in the chamber.
Control mechanism- If the sensor measures a current lower than expected, it signals the actuator.
Actuator- The battery sends an electric pulse to the electromagnet in the speaker, which then vibrates and creates sound.
What works well: It's very effective, beeps to warn residents that the battery is low
What doesn't work well: It can be triggered by steam from boiling water or a shower.

4. Stove/Oven Timer
In the dorm kitchens we have timers connected to the oven and stove that we must turn in order to use the stove or oven.
Sensor- Something senses whether the timer is at 0. I think it might be a tactile switch. After you twist the timer on, it slowly ticks back to 0 until a part taps the switch.
Control Mechanism- When the switch is triggered, a signal is sent to turn off the flow of electricity to the oven and stove.
Actuator- Wherever the electricity for the oven and stove comes from. When it's turned off, turning the oven to bake or the stove to high doesn't do anything. You must turn the timer to allow the electricity to flow again.
What works well: The timer prevents people from accidentally leaving the stove or oven on for long amounts of time and therefore increases the fire safety of the building.
What doesn't work well: The timer is really short so if you're trying to bake a cake or something, the oven will turn off in the middle and you'll have to restart it. This is especially bad if you don't realize it turned off and then find a pan of batter when you expect to find a cake. You should be able to set the timer for as long as you need.