Next time pleas include a small script that creates the table and inserts data instead of drawing a table. This will save time for anyone that tries to help you.

declare @tbl table (ID int, DEVICE int, VALUE int)

insert into @tbl (ID, DEVICE, VALUE) VALUES (9, 456, 70)

insert into @tbl (ID, DEVICE, VALUE) VALUES (8, 456, 60)

insert into @tbl (ID, DEVICE, VALUE) VALUES (7, 123, 70)

insert into @tbl (ID, DEVICE, VALUE) VALUES (6, 123, 60)

insert into @tbl (ID, DEVICE, VALUE) VALUES (5, 456, 50)

insert into @tbl (ID, DEVICE, VALUE) VALUES (4, 456, 10)

insert into @tbl (ID, DEVICE, VALUE) VALUES (3, 123, 50)

insert into @tbl (ID, DEVICE, VALUE) VALUES (2, 123, 20)

insert into @tbl (ID, DEVICE, VALUE) VALUES (1, 123, 10)

select t2.ID

from @tbl as t1 inner join @tbl as t2 on t1.ID = t2.ID -1

where t2.VALUE - t1.VALUE > 20

Adi