Standard&Poor's today has assigned its preliminary single-'B'-plus/single-'B'-minus rating to Protection One Alarm Monitoring Inc.'s Rule 415 shelf registration of$150 million debt securities. Also, Standard&Poor's has affirmed its single-'B'-plus corporate credit rating and single-'B'-minus subordinated debt rating of the company. The ratings reflect Protection One's stable and high-margin recurring revenue base and good cash flow generation. Offsetting these factors are the risks inherent in the company's high-growth strategy, its short operating history, thin interest coverage, and limited financial flexibility. With fiscal 1995 revenues of about $56 million, Culver City, Ca.-based Protection One focuses on the residential segment of the highly fragmented and consolidating security services industry, targeting the western United States. This geographic concentration helps the company