# CloudWatch alarms
<a name="cloudwatch-alarms-rule-action"></a>

The CloudWatch alarm (`cloudWatchAlarm`) action changes the state of an Amazon CloudWatch alarm. You can specify the state change reason and value in this call. 

## Requirements
<a name="cloudwatch-alarms-rule-action-requirements"></a>

This rule action has the following requirements:
+ An IAM role that AWS IoT can assume to perform the `cloudwatch:SetAlarmState` operation. For more information, see [Granting an AWS IoT rule the access it requires](iot-create-role.md).

  In the AWS IoT console, you can choose or create a role to allow AWS IoT to perform this rule action.

## Parameters
<a name="cloudwatch-alarms-rule-action-parameters"></a>

When you create an AWS IoT rule with this action, you must specify the following information:

`alarmName`  
The CloudWatch alarm name.  
Supports [substitution templates](iot-substitution-templates.md): API and AWS CLI only

`stateReason`  
Reason for the alarm change.  
Supports [substitution templates](iot-substitution-templates.md): Yes

`stateValue`  
The value of the alarm state. Valid values: `OK`, `ALARM`, `INSUFFICIENT_DATA`.  
Supports [substitution templates](iot-substitution-templates.md): Yes

`roleArn`  
The IAM role that allows access to the CloudWatch alarm. For more information, see [Requirements](#cloudwatch-alarms-rule-action-requirements).  
Supports [substitution templates](iot-substitution-templates.md): No

## Examples
<a name="cloudwatch-alarms-rule-action-examples"></a>

The following JSON example defines a CloudWatch alarm action in an AWS IoT rule.

```
{
    "topicRulePayload": {
        "sql": "SELECT * FROM 'some/topic'", 
        "ruleDisabled": false, 
        "awsIotSqlVersion": "2016-03-23",
        "actions": [
            {
                "cloudwatchAlarm": {
                    "alarmName": "IotAlarm", 
                    "stateReason": "Temperature stabilized.",
                    "stateValue": "OK",
                    "roleArn": "arn:aws:iam::123456789012:role/aws_iot_cw"
                }
            }
        ]
    }
}
```

## See also
<a name="cloudwatch-alarms-rule-action-see-also"></a>
+ [What is Amazon CloudWatch?](https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/) in the *Amazon CloudWatch User Guide*
+ [Using Amazon CloudWatch alarms](https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/AlarmThatSendsEmail.html) in the *Amazon CloudWatch User Guide*