Group Consecutive timestamps

Hi,

I have some trouble with grouping consecutive timestamps as 1. The Data is kind of alarmdata, so a row only appears when alarm is on. Every consecutive second it is "on" that means it is the same alarm that is still "on". So as you see:

timestamp 22:29:05 until 22:29:14 is consecutive. <---- one alarm = duration 9 seconds.  

timestamp 22:29:16 until 22:29:20 <--- other alarm. etc.

I would want to group the rows that have consecutive seconds. Therefor this table will consist of 4 different alarms. 
I think the best way is to creat a alarm starttime with the first timestamp per alarm and a column endtime.

Anybody that can help me with this?