Network Event Location System (NELOS) developed by AT&T provides estimated location information for cellular devices within their network. Law enforcement has become aware of this data and routinely requests it in search warrants when obtaining CDRs (Call Detail Records) of a subscriber. Some prosecutors are attempting to submit this data as accurate and reliable without supporting documentation from AT&T. In fact, the following disclaimer is on every page of NELOS reports provided by AT&T.

The results provided are AT&T’s best estimate of the location of the target number. Please exercise caution in using these records for investigative purposes as location data is sourced from various databases which may cause location results to be less than exact.

UPDATE: It appears the original NELOS system was shutdown with the 3G network; however, AT&T still provides historical precision location information in a similar format and it is still commonly referred to as NELOS. The current location system information provided by AT&T has the same concerns as the original NELOS system and should continue to be scrutinized.