Works on every lockscreen, that normally displays the next upcoming alarm. You need to press "update" at least once to make the app load your calendar and set the text on the lockscreen. Default Samsung lockscreen and HTC Sense lockscreen aren't such ones - nothing I can do about it until Samsung & HTC implement this standard feature in their modified lockscreens.
If you want the time of the events to be shown, change the date format in the app's settings (HH:mm for example).
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App icon: aboutpixel.de / © Bernd Boscolo