Use DescribeAlarmHistory with an AWS SDK or CLI

    /// <summary>
    /// Describe the history of an alarm for a number of days in the past.
    /// </summary>
    /// <param name="alarmName">The name of the alarm.</param>
    /// <param name="historyDays">The number of days in the past.</param>
    /// <returns>The list of alarm history data.</returns>
    public async Task<List<AlarmHistoryItem>> DescribeAlarmHistory(string alarmName, int historyDays)
    {
        List<AlarmHistoryItem> alarmHistory = new List<AlarmHistoryItem>();
        var paginatedAlarmHistory = _amazonCloudWatch.Paginators.DescribeAlarmHistory(
            new DescribeAlarmHistoryRequest()
            {
                AlarmName = alarmName,
                EndDateUtc = DateTime.UtcNow,
                HistoryItemType = HistoryItemType.StateUpdate,
                StartDateUtc = DateTime.UtcNow.AddDays(-historyDays)
            });

        await foreach (var data in paginatedAlarmHistory.AlarmHistoryItems)
        {
            alarmHistory.Add(data);
        }
        return alarmHistory;
    }

To retrieve history for an alarm

The following example uses the describe-alarm-history command to retrieve history for the Amazon CloudWatch alarm named "myalarm":

aws cloudwatch describe-alarm-history --alarm-name "myalarm" --history-item-type StateUpdate

Output:

{
    "AlarmHistoryItems": [
        {
            "Timestamp": "2014-04-09T18:59:06.442Z",
            "HistoryItemType": "StateUpdate",
            "AlarmName": "myalarm",
            "HistoryData": "{\"version\":\"1.0\",\"oldState\":{\"stateValue\":\"ALARM\",\"stateReason\":\"testing purposes\"},\"newState\":{\"stateValue\":\"OK\",\"stateReason\":\"Threshold Crossed: 2 datapoints were not greater than the threshold (70.0). The most recent datapoints: [38.958, 40.292].\",\"stateReasonData\":{\"version\":\"1.0\",\"queryDate\":\"2014-04-09T18:59:06.419+0000\",\"startDate\":\"2014-04-09T18:44:00.000+0000\",\"statistic\":\"Average\",\"period\":300,\"recentDatapoints\":[38.958,40.292],\"threshold\":70.0}}}",
            "HistorySummary": "Alarm updated from ALARM to OK"
        },
        {
            "Timestamp": "2014-04-09T18:59:05.805Z",
            "HistoryItemType": "StateUpdate",
            "AlarmName": "myalarm",
            "HistoryData": "{\"version\":\"1.0\",\"oldState\":{\"stateValue\":\"OK\",\"stateReason\":\"Threshold Crossed: 2 datapoints were not greater than the threshold (70.0). The most recent datapoints: [38.839999999999996, 39.714].\",\"stateReasonData\":{\"version\":\"1.0\",\"queryDate\":\"2014-03-11T22:45:41.569+0000\",\"startDate\":\"2014-03-11T22:30:00.000+0000\",\"statistic\":\"Average\",\"period\":300,\"recentDatapoints\":[38.839999999999996,39.714],\"threshold\":70.0}},\"newState\":{\"stateValue\":\"ALARM\",\"stateReason\":\"testing purposes\"}}",
            "HistorySummary": "Alarm updated from OK to ALARM"
        }
    ]
}

    public static void getAlarmHistory(CloudWatchClient cw, String fileName, String date) {
        try {
            // Read values from the JSON file.
            JsonParser parser = new JsonFactory().createParser(new File(fileName));
            com.fasterxml.jackson.databind.JsonNode rootNode = new ObjectMapper().readTree(parser);
            String alarmName = rootNode.findValue("exampleAlarmName").asText();

            Instant start = Instant.parse(date);
            Instant endDate = Instant.now();
            DescribeAlarmHistoryRequest historyRequest = DescribeAlarmHistoryRequest.builder()
                    .startDate(start)
                    .endDate(endDate)
                    .alarmName(alarmName)
                    .historyItemType(HistoryItemType.ACTION)
                    .build();

            DescribeAlarmHistoryResponse response = cw.describeAlarmHistory(historyRequest);
            List<AlarmHistoryItem> historyItems = response.alarmHistoryItems();
            if (historyItems.isEmpty()) {
                System.out.println("No alarm history data found for " + alarmName + ".");
            } else {
                for (AlarmHistoryItem item : historyItems) {
                    System.out.println("History summary: " + item.historySummary());
                    System.out.println("Time stamp: " + item.timestamp());
                }
            }

        } catch (CloudWatchException | IOException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }

suspend fun getAlarmHistory(
    fileName: String,
    date: String,
) {
    // Read values from the JSON file.
    val parser = JsonFactory().createParser(File(fileName))
    val rootNode = ObjectMapper().readTree<JsonNode>(parser)
    val alarmNameVal = rootNode.findValue("exampleAlarmName").asText()
    val start = Instant.parse(date)
    val endDateVal = Instant.now()

    val historyRequest =
        DescribeAlarmHistoryRequest {
            startDate =
                aws.smithy.kotlin.runtime.time
                    .Instant(start)
            endDate =
                aws.smithy.kotlin.runtime.time
                    .Instant(endDateVal)
            alarmName = alarmNameVal
            historyItemType = HistoryItemType.Action
        }

    CloudWatchClient {
        credentialsProvider = EnvironmentCredentialsProvider()
        region = "us-east-1"
    }.use { cwClient ->
        val response = cwClient.describeAlarmHistory(historyRequest)
        val historyItems = response.alarmHistoryItems
        if (historyItems != null) {
            if (historyItems.isEmpty()) {
                println("No alarm history data found for $alarmNameVal.")
            } else {
                for (item in historyItems) {
                    println("History summary ${item.historySummary}")
                    println("Time stamp: ${item.timestamp}")
                }
            }
        }
    }
}