The SDM 100 has been published since 1991. Its primary objective is to measure consumer dollars gained by alarm 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 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 an alarm company and its subscriber, and is typically the basis for valuation of an alarm company. RMR is the language of alarm company executives and is meaningful in comparative analysis among industry peers. Of the 100 security dealers ranked, 29 of them earned more than $1 million in RMR in 2009.