Apologies if this seems like an ad, but I feel as its the only type of product on the market its worthwhile knowing about.
(I work for Fireco by the way)
http://www.firecoltd.com/Fire/freedor.aspx
Wireless Swing Free device * Adjustable closing speed
* Wireless technology
* Operates up to power size 4 (80kg fire door)
* Allows a door to swing-free through whole range of movement
* Operates as a normal door until activated
* Suitable for right and left hand swing doors
* Can be installed on the opening or closing side of the door
* Night-time release facility
* Fail-to-safe technology, with a minimum battery life of 12-18 months
* Adjustable sensitivity
* Designed to comply with BS EN 1154, BS EN 1155, BS 7273-4 category C
* CE marked
http://www.firecoltd.com/Fire/freedor/how_it_works.aspxAny questions or comments?