Hatched at the Human Computer Interaction Lab at the Hasso Plattner Institute (HPI) in Potsdam, Germany, Ad Infinitum is a “parasitical” machine that, quite literally, lives off of human-generated energy. Housed in a rectangular acrylic tube with crank mechanisms (plus seats) at each end, the ‘off the grid’ device latches onto any curious visitor who sits down and reaches in: grab one of the mechanism’s leavers and a pair of cuffs that double as electrodes will ‘trap’ your arm in place and stimulate your wrist muscles with small electrical jolts. As the muscles contract, you involuntarily crank the mechanism’s leaver, generating kinetic energy the machine (or rather its battery) feeds on. Keep cranking and the machine will pause the stimulation, let go and the tingling shocks return. This ‘ad infinitum’ energy cycle is only broken – and the visitor freed – when another visitor reaches for the opposite leaver, thereby becoming the new host.