Some of the more important factors to consider include the offender population, financial and political commitment to EMHA, the structure of prisoner release that will best suit specific agency needs, and EMHA program evaluation based on recidivism statistics and other measures. In a programmed contact EMHA system, offenders are assigned to house arrest with some positive method of identifying their presence when the central computer places a phone call to the residence. Either a voice sample is recorded or a "tag" is attached that responds to an electronic inquiry; in some cases, a photograph of the offender is placed on an electronic file. This type of system is usually inexpensive and verifies the presence or absence of offenders only at the time of the central computer's call. A continuous signaling system usually consists of a transmitter that is attached to offenders and a receiver that is placed in offenders' residences. The receiver hears the transmitter up to a range of about 150-200 feet. When the receiver no longer hears the transmitter, the system assumes a departure has occurred. The receiver in the residence is usually accompanied by a microprocessor that has specific instructions on what to do if a change in status occurs. Some hybrid EMHA systems incorporate features of both programmed contact and continuous signaling systems. A dictionary of EMHA terms and a short history of electronic house arrest are provided.