Differentiating own accessories from those of others

A method implemented by a portable electronic device having a wireless short-range communication circuit:

• transmitting, by the portable electronic device to a mobile device, a first proximity message, wherein the portable electronic device is a portable tracking electronic device, wherein the first proximity message transmitted by the portable electronic device comprises a protocol identifier and a first derived hardware address, the protocol identifier specifying a derivation function used to generate the first derived hardware address, and wherein the first derived hardware address in the first proximity message is generated, by the derivation function, using a private key and first timing information;
• receiving a first reply from the mobile device that is paired with the portable electronic device;
• and
• transmitting a second proximity message comprising the protocol identifier and a second derived hardware address, wherein the second derived hardware address is generated, by the derivation function, using the private key and second timing information.