In the home multiple sensors i.e. Mica2/Mica2Dot motes will be placed who will track the members location. The motes should be placed so that all the places can be identified easily. According to the specification of Xbow the radio range of Mica2/Mica2Dot is around 150m i.e. 500 feet. However, different experiments by researchers show that until 100-150 feet apart the performance is reliable. Hence, we will use this range to place the sensors.

We will use a Grid Mesh topology to place the sensors so that they cover all the home. Crossbow recommends the following average mesh grid density:

• For 916 MHz Motes: 1 mote/2500 sq feet (50’ by 50’)
• For 433 MHz Motes: 1 mote/10000 sq feet (100’ by 100’)

Foliage and other RF obstacles will decrease distance. However, if the units are deployed such that motes can find other motes (parents) then the network will automatically reroute radio traffic.

Units are usually placed at least 1-3 feet above the ground. Placing units at ground level will decrease communication range. Different obstacles will also decrease distance.

Each member of the family will be tagged with a RFID or Mica2Dot. Mica2Dot/RFID with the persons will be programmed with an ID identifying the persons. The RFID/Mica2Dot will broadcast the ID after a predefined short interval. The sensors placed in the home will listen to this broadcast and send some location and identity related information to the central server. The central server will determine the exact positions of the persons.

RFID uses wireless technology operating with the 50 kHz to 2.5Ghz frequency range. Low frequency tags are a good choice for applications in which the distance between tag and reader is small (typically less than a foot) as opposed to UHF, which supports applications at greater distances (up to about 20 feet). VHF range (30 - 300 MHz) and the UHF range (300 MHz - 3 GHz). Mica2 mote can operate in 433 MHZ also in 915MHZ so it's compatible with RFID.

MPR 400/500 Crossbow’s mote processors (MPR 400 Mica2 or MPR 500 Mica2Dot) form the foundation of RFID and Asset Tracking solutions. These wireless network processor nodes can be integrated with multi-format RFID reader components (e.g., SkyeTek SkyeRead M1 Reader, www.skyetek.com) resulting in a low cost, mobile, networked RFID tag reader. Hence, we need RFID tagged with the persons and some RFID reader integrated with Mica2/Mica2Dot.