Using Passive RFID tags and UHF Readers for stock take
The read range of passive UHF systems may be as long as 12 m, so you must take this into consideration.

However, UHF RFID is also the most sensitive to interference, when compared to LF and HF RFID's. Interferences most commonly experienced with RFID systems result from environmental factors in the deployment.

Older tags mounted on metal or on containers of liquids both provide significant interference. 


  Recent developments in tag and antenna design and tuning have allowed
  these problems to be overcome provided they are considered at the
  planning stage. Also interference can be caused in UHF systems by
  reflection or re-radiation of power signals.


With proper expertise in this field such a system may be set up  according to your needs. This very much depends on your warehouse environment and how far away the readers and tags are from each other.

You may either get a professional to implement this system or else start off with a simple test: Try scanning products from a distance that is similar in your warehouse. If this works as expected, then you may proceed.