# `alarm_handler`
[🔗](https://github.com/erlang/otp/blob/master/lib/sasl/src/alarm_handler.erl#L22)

An Alarm Handling Process

The alarm handler process is a `m:gen_event` event manager process that receives
alarms in the system. This process is not intended to be a complete alarm
handler. It defines a place to which alarms can be sent. One simple event
handler is installed in the alarm handler at startup, but users are encouraged
to write and install their own handlers.

The simple event handler sends all alarms as info reports to the error logger,
and saves all in a list. This list can be passed to a user-defined event
handler, which can be installed later. The list can grow large if many alarms
are generated. This is a good reason to install a better user-defined handler.

Functions are provided to set and clear alarms. The alarm format is defined by
the user. For example, an event handler for SNMP can be defined, together with
an alarm Management Information Base (MIB).

The alarm handler is part of the SASL application.

When writing new event handlers for the alarm handler, the following events must
be handled:

- **`{set_alarm, {AlarmId, AlarmDescr}}`** - This event is generated by
  [`alarm_handler:set_alarm({AlarmId, AlarmDecsr})`](`alarm_handler:set_alarm/1`).

- **`{clear_alarm, AlarmId}`** - This event is generated by
  [`alarm_handler:clear_alarm(AlarmId)`](`alarm_handler:clear_alarm/1`).

The default simple handler is called `alarm_handler` and it can be exchanged by
calling `gen_event:swap_handler/3` as
[`gen_event:swap_handler(alarm_handler, {alarm_handler, swap}, {NewHandler, Args})`](`gen_event:swap_handler/3`).
`NewHandler:init({Args, {alarm_handler, Alarms}})` is called. For more details,
see `m:gen_event` in STDLIB.

### See Also

`m:error_logger`, `m:gen_event`

# `alarm`
*not exported* 

```elixir
-type alarm() :: {alarm_id(), AlarmDescription :: term()}.
```

# `alarm_id`
*not exported* 

```elixir
-type alarm_id() :: term().
```

# `clear_alarm`

```elixir
-spec clear_alarm(alarm_id()) -> term().
```

Sends event `clear_alarm` to all event handlers.

When receiving this event, the default simple handler clears the latest received
alarm with id `AlarmId`.

# `get_alarms`

```elixir
-spec get_alarms() -> [alarm()].
```

Returns a list of all active alarms. This function can only be used when the
simple handler is installed.

# `set_alarm`

```elixir
-spec set_alarm(alarm()) -> term().
```

Sends event `set_alarm` to all event handlers.

When receiving this event, the default simple handler stores the alarm.
`AlarmId` identifies the alarm and is used when the alarm is cleared.

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*Consult [api-reference.md](api-reference.md) for complete listing*