Many mobile phone users choose to share Advertiser ID information with app developers and social media companies. This includes precision handset geolocation information. Advertiser ID handset geolocation information is separate and distinct from handset geolocation information collected by cellular carriers, by Google for Android OS devices, or on iOS handsets in Significant Locations. Commercially available Advertiser ID information can be used during criminal investigations to determine if a handset was at multiple crime scenes near the times of those crimes and to determine specific locations where a handset was previously located. This webinar will discuss Advertiser IDs, show where Advertiser ID controls are located on iOS and Android OS handsets, outline investigative use and considerations, and detail specific instances when evidence collected from commercially available Advertiser ID information was used during the investigations of serious crimes.