Following changes over time in the nature of and response to school security incidents in New York City, significant changes were made to improve school security. An important development involved providing school guards with uniforms and radios. The guards received improved training and were deputized as special officers with arrest powers. Along with increased staffing, the New York City Board of Education has invested more money in security technology. Computerized card entry systems, for example, have been very successful in high schools. Students are given a photo identification card and, as they enter school, they are required to insert the card into a terminal. The computer determines if the card is valid, marks the student present for the day, and indicates if the student is "wanted" by a dean or guidance counselor. Personal alarm systems for staff have been placed in some high schools, along with burglar alarms that ring at a central station when activated. Closed circuit television has been tried in several large schools but with mixed results. During the 1991-1992 school year, 20 high schools and two middle schools were involved in a metal detector program. At the beginning of the 1991-1992 school year, New York City schools had 2,500 trained security officers deployed in more than 1,000 school buildings. By the end of the year, violence prevention workshops had been introduced in five schools.