In order to enable further developments in low cost wireless sensor networks (WSNs) for unobtrusive environmental monitoring, increased miniaturisation and integration of hardware is essential. This paper outlines the design concept and preliminary results for a multifunctional micromachined sensor unit, comprising CMOS-compatible temperature, humidity and gas sensors on a single silicon substrate. The sensor is being developed for integration with the highly modular and programmable Tyndall25 mote, where the "plug and play" stackable layers incorporate communications, power supply and on board data processing capabilities. This will enable the assembly of a miniature sensor network node complete with wireless transmission capability as well as intelligent data mining and storage. (c) 2008 Elsevier Ltd. All rights reserved.In order to enable further developments in low cost wireless sensor networks (WSNs) for unobtrusive environmental monitoring, increased miniaturisation and integration of hardware is essential. This paper outlines the design concept and preliminary results for a multifunctional micromachined sensor unit, comprising CMOS-compatible temperature, humidity and gas sensors on a single silicon substrate. The sensor is being developed for integration with the highly modular and programmable Tyndall25 mote, where the "plug and play" stackable layers incorporate communications, power supply and on board data processing capabilities. This will enable the assembly of a miniature sensor network node complete with wireless transmission capability as well as intelligent data mining and storage. (c) 2008 Elsevier Ltd. All rights reserved.