What does RFID mean for your property and evidence room

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Radio Frequency Identification (RFID) has the potential to keep track in a real time any item to which it remains attached in an open shelf storage area.


There are basically two varieties of RFID tags which can be attached to property or evidence items. One type is a passive tag. The other is an active tag.


Passive tags have a small “transponder” wire in them, basically an antenna with a small computer chip attached in the form of a self adhesive label. When it senses a radio wave the chip/antenna, “radios” back a unique ID number pre-programmed into the chip. The source of the radio signal is programmed to sense this number and record it. The source is typically a badge reader such as is used for building access. It can also be a mobile sensor. Users get within a short distance, depending on the size of the wire and the strength of the signal from inches to a few feet.


For longer range “reading” the active tag is superior. These tags differ from passive tags in being battery powered, the size of a key fob or larger and not amenable to attaching other than as “hang tags.” This allows them to receive and respond from many yards away.


The benefits of these tags for checking items out and back from a property room, by passing the tags near the sensor. In certain circumstances they can be useful for taking physical inventory. Users can take a portable sensor into the shelf area to sense items with in range, which are in open shelves. This can make possible a very rapid inventory. In a large warehouse the use of active tags can help track hundreds of items in an open area. They can even pinpoint the geographic coordinates of pallets of merchandise in a large, open Walmart warehouse.


There are disadvantages, however. The first is cost. Passive tags in large quantities are 10 to 20 cents each, but more in quantities of 100,000. Active tags are in the range of $10 to $50 each in such quantities. The mobile scanners tend to be in the range of $5,000 each and the fixed door scanners in the range of $2,500 to $5,000 each depending on features. The cost of using barcode tags and scanners is a small fraction of this cost.


A second problem is propagation. The radio signals do not penetrate metal or other sold substances such as densely stored items. The clay in paper used to store items will absorb the radio waves. In short items stored in metal shelves, especially the new high density shelves, much less filing cabinets, foil the ability to take the type of quick inventory that is possible in a wide open warehouse such as a Walmart distribution center.


Another problem is security. In an evidence storage area, when taking inventory a significant feature is the physical handling of each item to insure the integrity of its packaging. An RFID inventory which makes use of sensing electronic pulses rather that physically handling each item cannot guarantee that the item to which the RFID tag is suppose to be attached is actually there. The sensor may be reading a detached tag. Moreover, one of the points of pinpointing items in a physical inventory is to know exactly which shelf the item is on so that if an auditor visits, you can take him or her to the precise shelf where the item can be found. RFID sensing absent a very close range (inches) scanner can only provide tell the general area in which an item is stored, not the specific shelf. Uses will spend a good deal of time finding the items which auditors are seeking.


Used to check items in and out of the evidence room users will have to hold the items being transferred. In that case RFID holds little advantage over the cheaper and more convenient barcodes. Moreover, while barcodes are an enabling technology, they constitute but one component of an efficient, paperless property room.

Last update: May 23, 2018

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