Among other things, systems to encourage compliance with hand washing procedures can include: an infrared emitter that projects a first infrared beam with a transverse cross-section having a first axis and a second axis that is shorter than the first axis, the transverse cross-section having a maximum length along the first axis, the infrared emitter modulating the first infrared beam to transmit a first identification signal; wherein the infrared emitter projecting the first infrared beam is placed such that the first axis of the transverse cross-section of the first infrared beam is substantially parallel to a boundary.