Patent ID: 8558668

Claim:
A method for checking the proximity of one or more tags comprising: receiving a first message on a tag that is of a first type, that is broadcast at a regular time interval from a partner tag using a partner timer interrupt on the partner tag, and that includes a partner identifier of the partner tag that is used to distinguish the partner tag from other tags; reading the partner identifier of the partner tag from said first message on the tag; incrementing a number of tag encounters on the tag for said read partner identifier; sounding an alarm on the tag if said read partner identifier is in a list of sensitive tags on the tag; and broadcasting from the tag a second message that includes an identifier of the tag at the same regular time interval using a timer interrupt on the tag that the partner tag receives, uses to increment a number of partner tag encounters on the partner tag, and uses to sound an alarm on the partner tag if the identifier is in a partner list of sensitive tags on the partner tag, wherein the identifier is used to distinguish the tag from other tags.