Note acceptors are another good way to tell if a machine is empty.. If it's not offering to exchange notes then it's probably dead, likewise if you make one stop taking notes and then when you return it is taking notes try and change a £20 and if it still up for taking notes you know it's had a few dumped in and may be worth another go... Obviously on the same day otherwise it could have just been floated.
Good plan batman!!! note acceptor machines are now floated with a £250 float and they stop accepting notes at £125 :twisted: