A sign-in sheet is the form, on paper or a tablet, that an open house visitor fills in with a name and at least one contact method. It is the single most important tool at the event, because a visitor whose contact you did not capture cannot be followed up with, no matter how interested they were.
Good sign-in sheets ask for few required fields, keep rows big enough to read, and print a short line explaining why the visitor is being asked. Those three choices raise the share of visitors who leave a usable, real contact.
Paper and tablet sheets fail in different ways. Paper cannot be misconfigured and never runs out of battery, but it produces unreadable handwriting, lets each visitor see who came before them, and still has to be typed up later. A tablet fixes legibility, privacy, and the retyping, at the cost of a device you have to charge and lock down before doors open.