State Auditor General Jack Wagner, who Tuesday released a report disclosing that Pennsylvania had lost track of 923 of the state's 9,800 sex offenders, is among state officials calling for Pennsylvania to require five years of GPS monitoring for certain types of sex offenders, the Pittsburgh Post-Gazette reported Wednesday.

Worn as an ankle bracelet, GPS tracking devices can pinpoint a person's location using 32 federal government-operated satellites. But critics note the technology can fail in areas with tall buildings.

"Philadelphia is not a great place for GPS. Neither is downtown Pittsburgh," said Pennsylvania Probation Board spokesman Leo Dunn, who said their pilot project had encountered problems with false alerts.

But Wagner notes the technology is improving and is a more cost-effective alternative to incarceration of some sex offenders.