Synchronize several instances of Windows Form?

I have a Windows Forms Application project with one Windows Form, and it's called FormCheck. FormCheck has just one CheckBox.

This executable is copied in three devices, so now Joe, Mary and Larry each have a device with an EXE of this Windows Form.

How can I synchronize all 3 tablets so that when Joe clicks on the CheckBox all three devices reflect the checked CheckBox? And again, if Mary unchecks the CheckBox, all three tablets show an unchecked CheckBox in their device? I know I can use a Timer, but I don't want to use it so that's why I'm asking here.

For a similar question, someone suggested using signalR, but that's overkill for such an easy application.

Thanks.