Human beings live and work in close proximity to dangerous gases. Chemical accidents often cause considerable damages to human lives and properties, and their short- and long-term impact on the environment can be high. Hence, diligent monitoring and management of these gases are of profound importance. In industries where chemical accidents pose potential explosions and health hazards, wired sensors are installed in strategic locations. In some industries, employees are required to carry with them portable sensing devices in addition. Still, achieving high spatio-temporal resolution is challenging, since dense deployments impede the mobility of employees, robots, or other mobile objects. In this article, we propose the use of nanotechnology and wireless sensor networks for monitoring toxic gases. Nanotechnology offers the possibility of developing gas sensors having small form-factors and high sensitivity. Wireless sensor networks enable high spatio-temporal sensing, in-network processing, and multihop communications. The article shares our experience with a wireless sensor network monitoring ammonia. The network consisted of 21 sensor nodes, four of which integrated arrays of ammonia sensors while the rest served as intermediate nodes.