A temperature monitoring service in which remote monitoring units are distributed to customers who then set up monitoring as desired at their facilities. The devices may be registered through a web site using the Internet. Monitoring information may be communicated using a publicly available, wireless network, such as a cellular telephone network. The service may be provided with a system, including a server, which can deliver high levels of monitoring functionality. The server may support streaming monitoring information to a customer for analysis or sending a command activating a device connected to a remote unit. Remote units associated with the same location may be in a pool, comprising one active unit and one or more spare units, in which the server automatically identifies the active unit. The server may support analyzing monitoring information according to an expected cycle pattern of a ventilation system at the monitored facility.