Tracer Disk

These are small ceramic disks, about the size of a human palm, perforated down the center and covered with runes. A tracer disk's magic is activated by snapping it in half down the perforation. Thereafter, it is possible to find one half of the disk using the locate object spell at an unlimited distance – provided the caster has the other half of the disk in their possession. It's not generally feasible to use a tracer disk to monitor a person – they are large enough that sneaking one into a target's pocket would be difficult and noticeable – but they are commonly snuck into baggage or onto vehicles as tracking devices. Of course, one danger of using tracer disks is that the connection goes both ways: if the disk is discovered, a spellcaster could just as easily use the locate object spell to follow the missing half of the disk back to its owner.

Once broken, a tracer disk has a limited capacity of magic, and is useless once the spell ends. The duration varies according to quality of manufacture, but they generally last about a month.