Item for alarm clocks etc. and daylight saving time

Setup, Configuration and Use Beginners
1

I have some items which define the time for stuff like alarm clocks. Only the time is relevant, I don’t care about the date. But as there are only DateTime items I use those.

Depending on how I set the time, the date of those items is either 1970-01-01 or the date when the time was last set.

Now the trouble starts, as depending on the date the time zone is MET or MEST. When I now use the item to trigger a rule (with only the time) openhab seems to match the UTC time and depending on the timezone of the item and the current time zone the alarm goes to 1 hour too late or too early.

Is this the expected behavior? How can I use items as triggers which are not updated daily?

2

The time-only usages of DateTimeType can be a bit tricky and in some cases error-prone when the epoch offset becomes negative because of the difference between the system or openHAB time zone and UTC.

  • Which time zone have you configured in openHAB regional settings?
  • Which time zone is configured for your system/OS?
  • Do you have a time zone configured in JAVA_EXTRA_OPTS (if so, which one)?
  • How do you set the item state? You write “depending on how I set the time”. Perhaps you can walk us through a concrete example where you set it in some specific way and get a specific (unexpected) result.
  • What does your rule look like?

See also How to fix Incorrect datetime value '1970-01-01 01:00:00' error with MySQL TIMESTAMP in OpenHAB JDBC Persistence? - #7 by laursen

3

Hopefully you solved your ME(S)T trouble.

You can easily use the time of a DateTime Item to trigger a rule like this:

DateTime Clock_10  (gClock) // in my case: 2026-03-18T22:30:00.000+0100

rule "Beleuchtung: Aussenleuchten 22:30 aus"
when 
    Time is Clock_10 timeOnly     
then 
    //do something
end

rule triggers every day.

happy Easter

4

  • Regional settings: (GMT+1:00) Europe/Berlin

  • System is Linux, so the clock runs in UTC but timezone is set to (GMT+1:00) Europe/Berlin

  • No JAVA_EXTRA_OPTS but TZ is set in docker-compose:

        openhab:
        container_name: openhab
        image: openhab/openhab:5.1.3
        restart: unless-stopped
        network_mode: host
        volumes:
            - /etc/localtime:/etc/localtime
            - /etc/timezone:/etc/timezone
            - /opt/openhab/addons:/openhab/addons
            - /opt/openhab/conf:/openhab/conf
            - /opt/openhab/userdata:/openhab/userdata
            - /opt/openhab/persistence:/openhab/persistence
            - /opt/openhab/backup:/openhab/backup
        environment:
            - CRYPTO_POLICY=unlimited
            - TZ="Europe/Berlin"

  • I have tried different input methods as nothing works especially well in Firefox

    • This one takes the time as UTC 1970-01-01

                - component: f7-col
            slots:
              default:
                - component: oh-input
                  config:
                    clearButton: false
                    inputmode: text
                    outline: true
                    variable: time
          - component: f7-col
            slots:
              default:
                - component: oh-button
                  config:
                    action: command
                    actionCommand: =vars.time
                    actionItem: =props.item

    • rlk_datetime_standalone (from marketplace) uses the current date / timezone but the value also seems to be stored as UTC. So if I set the value now to 7:00 it is stored as 5:00 UTC which is 7:00 MEST but 6:00 MET

  • My rule trigger looks like this (created in the gui):

    configuration: {}
triggers:
  - id: "1"
    configuration:
      itemName: automation_wecker
      timeOnly: true
    type: timer.DateTimeTrigger

What is unclear to me: How are time-only items supposed to work? If the DateTime is stored in UTC they need to be updated at each daylight saving time change.
Thanks for your help!

5

Let’s try to isolate the problem. I know nothing about widgets/UI components, so I’d like to keep that out of the equation for now. I did the following

  • openHAB time zone: Pacific/Midway (GMT-11)
  • JVM time zone: Europe/Copenhagen
  • Item: DateTimeTest

Created these DSL rules:

rule "DateTimeTest set"
when
    Item DateTimeTest changed
then
    logInfo("TZ", "jvm.zone = {}", ZoneId.systemDefault)
end

rule "DateTimeTest triggered"
when
    Time is DateTimeTest timeOnly
then
    logInfo("Triggered", "DateTimeTest triggered")
end

Then did this in a karaf console (time was one minute later):

openhab:update DateTimeTest 16:50

With this result:

2026-04-03 16:49:06.018 [INFO ] [openhab.event.ItemStateChangedEvent ] - Item 'DateTimeTest' changed from NULL to 1970-01-01T16:50:00.000+0100 (source: org.openhab.core.io.console$openhab)
2026-04-03 16:49:06.020 [INFO ] [org.openhab.core.model.script.TZ    ] - jvm.zone = Europe/Copenhagen

And then:

2026-04-03 16:50:00.020 [INFO ] [.openhab.core.model.script.Triggered] - DateTimeTest triggered

I believe only the JVM time zone is relevant here, not the time zone configured in openHAB. The “Time is” creates a cron expression using the JVM time zone:

I guess this is because the JVM time zone is used in the other end when evaluating cron expressions.

In any case, it seems to work fine for me. I suspect that you may lack to set up the JVM time zone for your Docker container.

Can you try to run these same tests and post the results?

6

See also Rule based on CronJob does not execute (OH3.2, Synology DSM > 7.0, Docker) - #9 by JimH

7

Without changing anything in the config I got this:

2026-04-06 11:56:34.714 \[INFO \] \[org.openhab.core.model.script.TZ    \] - jvm.zone = GMT

(I seem to have disabled the change events somewhere, so i only got the log from the rule.)

Next I tried to add EXTRA_JAVA_OPTS to my docker-compose file and while doing so I realized that I have a syntax error. This does not work:

            - TZ="Europe/Berlin"

I have to use either

            - TZ=Europe/Berlin

or

            TZ: "Europe/Berlin"

Now I get:

2026-04-06 14:17:22.396 \[INFO \] \[org.openhab.core.model.script.TZ    \] - jvm.zone = Europe/Berlin 
2026-04-06 14:18:00.379 \[INFO \] \[.openhab.core.model.script.Triggered\] - DateTimeTest triggered

and the rule actually triggers at the correct time.

Thanks a lot for your support!