I'd like to find an e-ink display, maybe 4 inches square, that would be either entirely black or entirely white - to indicate if the postman has been here today yet.
I live in a condominium cul-de-sac with 18 units. The mailboxes are at the head of the cul-de-sac, and I want to design a system that will detect the postman when he arrives, and display an indicator that everyone can see either driving by the mailbox installation, or from their porch.
I don't want the indicator to consume any power except when its state is changing, so I thought maybe an e-ink display could be set to black before he arrives, and to white or red after that. Such a display could have essentially zero resolution, and very slow refresh rate. And of course I don't want to spend anything significant for it.
Does such a display exist?