Because electronic monitoring provides greater control than does probation while offering relief to prison crowding, experts predict widespread use. The device was the brainchild of a New Mexico judge, Jack Love, with inspiration from the "Spiderman" comic strip. They are typically small, black, plastic boxes that strap onto the wrist or ankle of a detainee. The kind used to monitor Dr. Avol, a convicted negligent landlord in Los Angeles County sentenced to detention in his own decrepit apartment building, sent out a computer signal over telephone lines if he strayed more than 150 feet away from the building. Another design requires a detainee to plug an electronic "key" into his telephone when a special computer calls to check on him. One detainee states that electronic monitoring keeps him detained to his yard whereas earlier regular probation had allowed him to leave to get cigarettes. Every 600 offenders detained in this way yields an estimated $40 to $50 million dollar savings in prison costs.