Environment +and DST Changes

This section explains the effect on alarms due to the environment and DST +changes.

Environment Changes

An environment change typically +involves change in the system time/date, workdays or UTC offset, and due to +this, alarm's expiry time can be put in the past.

When an environment +change occurs, the Alarm Server can respond in any of the following ways:

The Alarm Server queues the alarms that have been skipped. These alarms +then expire immediately and must be acknowledged by the device user.
The Alarm Server uses KSkippedAlarmInstancesPubSubKey P&S +key to notify the clients about the skipped calendar alarms. This key can +be used only by the device creators.

Alarm Server observes changes in the UTC offset as a locale change +since the UTC offset is set according to the localized position. It observes +this offset from the system, and on change of this offset, only the alarms +in the alarm queue that are based on the floating time undergoes changes.

NOTE: +All alarms in the alarm queue are re-evaluated only if system time/date and +workday changes. This is applicable for all alarms irrespective of their time +formats. The workday changes are also a locale change for the system.

Daylight Saving Time Changes

Daylight Saving Time +(DST) or Summer Time, is a way of utilizing more daylight by advancing the +local time by one hour during the summer.

The clocks are adjusted +forward by one hour at the beginning of spring and are adjusted backward in +autumn. The time adjusted backward by one hour in autumn is usually referred +as Standard Time (or Winter Time). In a typical case where a one-hour shift +occurs at 02:00 local time, the clock is adjusted forward from 02:00 standard +time to 03:00 DST in spring and that day has 23 hours. Whereas in autumn, +the clock is adjusted backward from 02:00 DST to 01:00 standard time, repeating +that hour, and that day has 25 hours.

Alarm Server observes this DST +event from the Time Zone Server using KDSTChangePropertyKey P&S +key. This key can be used only by the device creators. On receiving notification +of this event through the key, all alarms (based on the floating time format) +in the alarm queue are re-evaluated for their expiry time.