German police reportedly use a technology called silent SMS to track down crime suspects.
According to a presentation given at the 28th Chaos Communication Congress in Berlin, Germany, 440,783 such "stealth" messages were sent by federal police authorities as well as the Bundesamt für Verfassungsschutz, Germany's equivalent of the FBI, in 2010. According to Heise Online, Germany's customs have picked up silent SMS as a tracking method, which is likely to result in a substantial increase in the use the technology. The customs alone sent 227,587 silent SMS in the first half of 2011.
German authorities apparently use silent SMS to create a movement profile of suspects or locate their position. SMS pings are received by a cellphone, but the user will not be notified of it. However, the cellphone carrier will record the data in a log, which can be requested by the government. While the data do not provide information about the phone, they do deliver location data via the cell towers that were used when the silent SMS was sent.