The tags would be located in places where a reader would not be readily available. Could a timestamp be triggered by a battery-powered input, such as simply pressing a button?
Passive ultrahigh-frequency (UHF) RFID tags lack their own internal clock mechanism, so there would be no way for such a tag to do this on its own without a reader sending that information to the tag. Some passive UHF and high-frequency (HF) chips do have an i2C connection, which is like an input-output port that can link the transponder to another electronic device. So you could potentially connect a device with the capability of transmitting the date and time to the tag. You would need to contact chip manufacturers to request information about how to send data to the tag via the i2C connection.
—Mark Roberti, Founder and Editor, RFID Journal