We have a bird feeder, which squirrels cannot (usually) get to but they hang out nearby to eat what falls out. We also have the occasional feral cat or two that swing by. I can attest that they are all listening to each other sound the alarm, so it makes sense they would also listen to the "all clear".
My wife also does, because if they sound the alarm that means a cat is nearby, and she comes over to the window to see if she can see the cat. This may have caused me to pay more attention to the whole interaction.
Sorry, didn't see the reply until now. I have a nothing special bird-feeder, but two things make it harder for squirrels to get to:
1) it is suspended, from high above, by a rope around a tree branch; it is high enough that they cannot jump up to it from below (well, it is high enough now, anyway, since I saw them doing that)
2) just above the bird feeder is a dome, with a hole in the center, through which the rope passes. There is a stick which the rope is tied around, which keeps the dome just above the bird feeder. If the squirrel climbs down the rope from above, the dome keeps them from getting to the bird feeder.
My wife also does, because if they sound the alarm that means a cat is nearby, and she comes over to the window to see if she can see the cat. This may have caused me to pay more attention to the whole interaction.