PL/SQL :: Count Sequential Events

I have a table with around half a million rows. I would like to determine how many sequential events occur per device per unique group of events. The requirement is that the events continue to occur within 1 second of each other, every second, with no gaps. For example, in the sample below there is a sequence of 2 events for device 2737, and another sequence of 5 events for device 2737. If there was a 1 second interval with no event (Signal_time) then that would be the end of one group of events, this is also shown below.

Using Oracle 11.2.0.2.0

DEVICE_ID     SIGNAL_TIME
4401     17-JUN-12 12.59.59 PM
2332     02-MAY-12 12.59.59 PM
1086     30-MAY-12 12.59.58 PM
2737     17-JUN-12 12.59.58 PM -- start of one group / sequence of events
2737     17-JUN-12 12.59.58 PM -- end of one group / sequence of events

[Code]...

-- start of one group / sequence of events

2737     16-JUN-12 11.59.59 PM
2737     16-JUN-12 11.59.59 PM
2737     17-JUN-12 12.00.00 AM
2737     17-JUN-12 12.00.01 AM

-- end of one group / sequence of events

2737     17-JUN-12 12.00.03 AM

-- this is excluded from the above group of 5 events, but this may be the start of another group

Required output

Device--Count(*)--Start_Signal_Time-----------End_Signal_Time------------Duration (seconds)
2737----5-------------16-JUN-12 11.59.58 PM---17-JUN-12 12.00.01 AM--4
2737----2-------------17-JUN-12 12.59.58 PM---17-JUN-12 12.59.58 PM--1