The SDM 100 has been published since 1991. Its primary objective is to measure consumer dollars gained by security companies, in order to present an account of the size of the market captured by the 100 largest security providers. SDM 100 firms are ranked by their recurring monthly revenue (RMR). RMR is the amount of contractually recurring revenues due from customers, for such services as monitoring, contracted service and system maintenance, and leasing of security systems. It is the revenue associated with the contractual agreement between a security company and its subscriber — derived from customer billing for services such as monitoring, contracted service, managed solutions, and leasing of security systems — and is typically the basis for valuation of a security company. RMR is the language of security company executives and is meaningful in comparative analysis among industry peers. Of the 100 companies ranked, 33 of them earned more than $1 million in RMR in 2010. Below is the list of the SDM 100 companies in alphabetical order.