3 ms·
There are already solutions, e.g. http://startingline.en.alibaba.com/product/502176603-212131584/personal_alarm_device_Credit_Card_RFID_key_finder_beep_alarm.ht
by JoachimSchipper 15y ago
There are already solutions, e.g. http://startingline.en.alibaba.com/product/502176603-212131584/personal_alarm_device_Credit_Card_RFID_key_finder_beep_alarm.html http://startingline.en.alibaba.com/product/502176603-2121315.... I'm sure you can find more, RFID seems a rather obvious technology for this kind of thing.