Those of you are looking for wireless sensors with zero power wireless transceivers than Maxim is doing just that for you. They have designed 2.4GHz Wireless Transceivers -Zero External Power. These tiny wireless transceivers work on small Lithinum battery for life and you never replace that battery or it can come factory mounted in the casing.
Current design is OOK type, but soon they have other types as well. You can finds their wireless designs here
http://www.maxim-ic.com/Wireless.cfm
Maxim also makes high data rate transceivers up to 11MBPS and dual band.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4532/CMP/BTDT
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Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.