  Personal item tracking devices are popular for locating lost items such as
keys, wallets, and suitcases. Originally created to help users find personal
items quickly, these devices are now being abused by stalkers and domestic
abusers to track their victims' location over time. Some device manufacturers
created `anti-stalking features' in response, and later improved on them after
criticism that they were insufficient. We analyse the effectiveness of the
anti-stalking features with five brands of tracking devices through a gamified
naturalistic quasi-experiment in collaboration with the Assassins' Guild
student society. Despite participants knowing they might be tracked, and being
incentivised to detect and remove the tracker, the anti-stalking features were
not useful and were rarely used. We also identify additional issues with
feature availability, usability, and effectiveness. These failures combined
imply a need to greatly improve the presence of anti-stalking features to
prevent trackers being abused.
