Each system includes a tripod, network HMI, gas detection sensor(s), and alarm warning devices. An optional Sentinel SiteWatch provides remote access to system data via Ethernet or cellular communication. Power to the sensor assembly is supplied by a rechargeable Smart Battery Pack, disposable batteries or directly from HMI. Flexible and expandable, a Site Sentinel network can include up to 32 devices and consist of any combination of wireless and/or wired sensors, one or more HMI panels and optional solar panels. Additional sensors and/or remote alarm stations on tripods can be added as needed to assure widespread alert to site personnel.