The invention provides an anti-lost device applied to people, objects in a determined relative space anti-lost range and other anti-lost objects. The anti-lost device comprises an identification device and a monitoring device. The identification device comprises a passive RFID label, and the monitoring device comprises a passive RFID label reading or reading-writing module, a reminding module and a power module. The reminding module is triggered to make a response when the reading module monitors or does not monitor the passive RFID label, two kinds of monitoring devices can be combined for use, the identification devices also can be related or paired for use, and reminding modes comprise sound, light, actions and the like, wherein linked reminding is carried out. The anti-lost device can be made to the shape of a bracelet and other wearable objects or can be made to the shape of a card or a button so that the anti-lost device can be conveniently carried, and the anti-lost device can comprise a back adhesive face and other attachable structures or bolts and other fixed connection structures to be conveniently fixed on other devices. Due to the passive RFID label, the identification device does not need a power source, cost is greatly lowered, reliability of the anti-lost device can be enhanced, the anti-lost effect is ensured, and the service life of the anti-lost device is obviously prolonged.