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  2. Reed switch - Wikipedia

    en.wikipedia.org/wiki/Reed_switch

    The reed switch [i] is an electromechanical switch operated by an applied magnetic field. It was invented in 1922 by professor Valentin Kovalenkov at the Petrograd Electrotechnical University , [ 1 ] and later evolved at Bell Telephone Laboratories in 1936 by Walter B. Ellwood into the reed relay.

  3. Security alarm - Wikipedia

    en.wikipedia.org/wiki/Security_alarm

    Reed Switch. The hermetically sealed reed switch is a common type of two-piece sensor. This switch operates with an electrically conductive switch that is either normally open or normally closed when under the influence of a magnetic field in respect to proximity to the second piece, which contains a magnet. When the magnet moves away from the ...

  4. Electromagnetic door holder - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_door_holder

    An electric current typically energizes the electromagnet to attract and hold the steel plate, keeping the door open. Unlike electromagnetic locks, the magnetic attraction of an electromagnetic door holder is usually weak enough that it can be manually overpowered at any time by anyone, allowing the door to close. [citation needed]

  5. Electromagnetic lock - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_lock

    Given the relative permeability of a material can vary from around 250 for cobalt to around 5000 for soft iron and 7000 for silicon-iron, the choice of magnetic core can therefore have an important impact upon the strength of a magnetic lock. Also relevant is the choice of current, number of loops and effective length of the electromagnet.

  6. Electric bell - Wikipedia

    en.wikipedia.org/wiki/Electric_bell

    Fire alarm bell. Fire alarm bells are divided into two categories: vibrating, and single-stroke. On a vibrating bell, the bell will ring continuously until the power is cut off. When power is supplied to a single-stroke bell, the bell will ring once and then stop. It will not ring again until power is turned off and on again.

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