Look up / google RFID tags, (radio frequency identification tags) they are widely used in industry attached to products , especially cars on production lines, they carry all the data about the car, colour, upholstery spec, wheels etc. And are interrogated at each production station. The passive chips carry no power supply, they are interrogated by receivers which supply power via the radio signal ( only work at a very short range)
When used as keyless entry, the transmitter / receiver in the car is always on standby to interrogate a passing card / fob.
Chips can be passive, short range device powered by the radio signal, or active powered by battery which gives them much longer range. Think of RFID tag as a transponder which transmits information when activated by suitable wireless signal.
The keyless cars are notoriously easy to steal, if the card / fob is anywhere near house wall or door it can be activated by one scanner, it then transmits code to another device near the car which unlocks car and allows it to be started - once started it can be driven away with no card present.
Security people reckon you should keep fob in a faraday cage (wrap in aluminium foil or keep in purpose made metallized pouch which are also useful for keeping your contactless credit and debit cards in) - even a metalised plastic crisp packet will do LOL . Nothing that uses wireless or is connected to internet can ever be secure.