A fundamental mechanic in ZWERM was the check-in, which could be performed with one of the 1441 RFID cards that were distributed among different households in the 2 participating neighborhoods. The households were selected by walking through the neighborhoods and posting envelopes containing a RFID card and a leaflet explaining the goal and functioning of the system in every encountered letter box.
Check-ins were performed on 2 “Hollow trees”, placed at a physical location that was central to each neighborhood. These trees were 3 meters high and custom made for ZWERM. They contained a touch-enabled PC made for outdoor use, an RFID reader and a battery to power the PC and the RFID reader.
There were two types of check-ins. The solo check-in was performed by a single user and scored the player 10 points. The combo check-in was performed by two players from the same team who had never checked-in together during the current campaign and gained both players 50 points. The check-in mechanism with the RFID cards was simple and inclusive. It allowed people who did not own a PC, tablet or smartphone to participate in ZWERM. All they needed was their RFID card.