These squirrel proof bird feeders spin from the weight of a squirrel. They either spin the entire feeder or the platform where the birds stand on.
One such type of device that is the Squirrel Stop or Twirl a Squirrel. It can be used with any existing bird feeder and spins for 20 seconds. However, if you have a bird feeder that is easy to grab on to, some squirrels can hold on to the feeder so it doesn't work 100% of the time.
See this type of squirrel deterrent in action:
The other type of spinning bird feeder has the spinning mechanism built in. It spins much faster so the squirrel has a harder time hanging on. Most of the time, they will spin off in a matter of seconds.
As you can see here, this squirrel gives puts up a good battle and holds on a good bit, but the bird feeder still wins.
One such type of device that is the Squirrel Stop or Twirl a Squirrel. It can be used with any existing bird feeder and spins for 20 seconds. However, if you have a bird feeder that is easy to grab on to, some squirrels can hold on to the feeder so it doesn't work 100% of the time.