Other Monitors

A typical baby monitor, sometimes also known as a baby alarm, is a simplex (uni-directional) radio transmitter and receiver system used to remotely listen for noises made by an infant. more...

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The transmitter, equipped with a microphone, is placed near to the child and the receiver, equipped with a speaker, is carried by, or near to, the person caring for them at the time. Some baby monitors are duplex (bi-directional), using transceivers that allow the caregiver to communicate back to the baby, and some have a feature allowing music to be played on the transmitter (and thus played to the child).

One of the primary uses of baby monitors is when the infant is asleep in a separate room, allowing caregivers to keep track of any problems while away from the baby.

Technologies

Baby monitors may incorporate a visible signal as well as repeating the sound. This is often in the form of a set of lights to indicate the noise level, allowing the device to be used when it is inappropriate or impractical for the receiver to play the sound. Some modern baby monitors also incorporate a digital camera to show video footage on the receiver in a similar method to web cams, and some others allow the receiver to be plugged into a television; generally, they are called baby cams. Some devices also incorporate movement sensors on the transmitter allowing it to warn caregivers of possible sudden infant death syndrome. Other monitors have a vibrating alert on the receiver making it particularly useful for people with hearing difficulties.

It is common for the receiver to use batteries as their source of power allowing it to go with the caregiver. The transmitter stays with the infant crib and is usually plugged into a socket. Some baby monitor packages include two receivers.

The frequency used by the devices usually lies in the range of 49–50 megahertz, though some models can go as high as 900 MHz. As with all wireless transmission systems there is the possibility that a receiver used by a third party could pick up the transmissions. To aid this many models allow a choice of bands.

There have in the past been baby monitors that used a length of cable (around 100 m) instead of radio or, alternatively, using mains wiring.

Read more at Wikipedia.org