These are two types of contacts widely used in electrical installations and circuits. Distinguishing the difference of these two types is very simple.

• A NO (normally open) type contact is one that does not let the current flow while the same or the device is in standby or standby mode. The most common type NO contact is eg house switches, which remain open (not closedCircuit) until the switch is pressed.
• The NC contacts (normally closed) are the opposite of the NO contact, they let the current pass while they are in standby or at rest to be actuated. An example would be a thermal protection relay of a motor, which remains closed while there is voltage.

The electrical mechanisms are indispensable in any installation of a house, office, etc. The mechanisms can be of several types depending on where the installation is performed.

• Recessed interior mechanisms: Ideal for indoor use.
• Mechanisms of interior in surface: Ideal for the use in interiors without necessity to realize work.
• Exterior mechanisms: Ideal for outdoor use andGarages

Within each type of installation is where we can find different mechanisms depending on the function we need. The most common electrical mechanisms in an electrical installation are:

1. Simple switch: The mechanism that serves to turn the light on or off at one point.
2. Switch: This is the same mechanism above, but this allows to turn the light on or off from two points diIngs.
3. Crossover switch: Same as above but allows turning off and on the light from three different points.
4. Pushbutton: Normally used for timbres or steps with light and on/off timer.
5. Regulator: It allows to control the level of power of light.
6. TV socket TDT/SAT: Connections for TV, radio, and/or satellite connection.
7. Base schuko: TomaCurrent based on neutral, line and ground.
8. Telephone or network socket: Bases for telecommunications, networks or telephone.

Within the detection systems we can find different types according to their operation, among them the most common:

1. Infrared sensors
2. Vibration sensors.
3. Photoelectric sensors.
4. Ultrasound sensors.
5. Acoustic sensors

Each type of sensor uses different detection methods and each one is recommended according to the situation.

1. Sensors by infraRrojos, are one of the most used types, thanks to its reliable operation and installation, since we can find this type of wired and wireless sensors.
   The infrared sensor has a phototransistor capable of detecting the infrared electromagnetic radiation emitted by a body, this type of radiation is not visible by the human eye. A change of radiation in its perimeter will activate the relay and proceed to send ato alarm signal.
   Within these, there are two models, passive infrared sensor, which only has a phototransistor and assets, which have an emitter and a receiver.
2. Vibration sensors are used mostly in security systems, such as window sensors. car alarms etc.
   Its operation is based on an accelerometer, through a piezoelectric sensor. This type of sensorDue to its construction material it allows to detect changes and pressure when emitting an electric charge.
3. Photoelectric sensors, these are the sensors that use photoelectric rays, normally a transmitter and a receiver are used, they are commonly used in automatic door systems, elevator doors, production chains, etc.
4. The ultrasonic sensors are those that emit an acoustic signalabout 30 kHz, a signal that is not appreciated by humans. This signal or wave propagates through space, walls, objects, doors, etc. once the signal has spread the sensor is activated and any change will trigger the sensor.
   These types of sensors are also used in devices that require measuring distances and detecting objects.
5. Acoustic sensors, are those that can detect the signal emitted by anyobject and are able to detect the pressures that the acoustic waves emit, such as the noise of the crystals when breaking a window.