Vaccines contain microchips or nanochips that track vaccinated individuals' locations and behaviour.
This 2020-era conspiracy theory confuses science with fantasy. The smallest microchips commercially available are still 0.5 millimetres, roughly the size of a grain of salt, and cannot fit through hypodermic needles (which are about 0.3 millimetres in diameter). More fundamentally, any implantable tracking device requires a power source and antenna to transmit, which would generate electromagnetic radiation detectable by simple equipment. Scientists at MIT and Stanford have created microscopic devices ('microchips' just micrometers in size), but these are experimental, require external power to function, and exist only in controlled laboratory settings. The technology to achieve what conspiracy theorists imagine, imperceptible, wireless, powered devices in bloodstreams, violates fundamental laws of physics. X-ray imaging of vaccinated individuals would immediately reveal any foreign object, yet millions of chest X-rays and CT scans have been performed without finding anything. This myth flourished during the COVID pandemic when legitimate questions about vaccine safety were exploited by bad-faith actors.