> For the complete documentation index, see [llms.txt](https://docs.globalalerting.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.globalalerting.com/monitoring-and-response/working-with-devices/devices-explained.md).

# Devices Explained

A device represents an object that sends messages to and / or receives messages from GAP.

A device can be anything that has a mechanism for sending and / or receiving data (including satellite phones, GSM (cellular) trackers, smartphone apps, etc.).

Like all data in GAP, a device resides in a tenant.

## Device Types

Each device is of a specific device type.  A device type is usually a manufacturer / model combination (e.g. Iridium Extreme, Garmin inReach Mini, NAL SHOUT Nano, etc.).

The type of the device determines its features (e.g. text messaging, remote configuration, address book synchronisation, etc.).

See the [list of supported device types](/monitoring-and-response/working-with-devices/supported-devices.md) for more information.

## Bearers

A bearer is the means by which a device sends its data to GAP - for example, Iridium SBD, Globalstar, UDP, TCP, etc.

A device type will support one or more bearers.

## Messages

A message is a piece of data sent from a device to GAP (or from GAP to a device).

Messages sent from a device to GAP are known as Mobile Originated (MO) messages.

Messages sent to a device by GAP are known as Mobile Terminated (MT) messages.

## Message Types

Message Types determine the meaning (and sometimes the content) of messages.

For example, a message of type "FreeText" will typically contain a text message composed by the device user or GAP Portal operator.  A message of type "CheckIn" will represent a proactive notification from the device user that they are OK (and will typically contain position data).

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