Ok heres some questions for you to answer to help you define the outcomes that you may require

first

1. define the sensor type To measure the weight - assumption person will step on sensor

doing a quick google - check out sensors

http://www.kerrmedical.com/weightsen...mmonitors.aspx

http://www.medicalproductsdirect.com/alprmasmwese.html

simple pressure mat cant measure weight
http://www.jaycar.com.au/productView.asp?ID=LA5131


2. pick an pic which will allow a analog input , most do ,these type of mat produce a voltage relative to a weight so hooking it up is easy enough as most provide details of the interface to most alarms system they support.

get that far and it s a starting point