the following detailed description of preferred embodiments of the invention will be made in reference to the accompanying drawings . in describing the invention , explanation about related functions or constructions known in the art are omitted for the sake of clearness in understanding the concept of the invention , to avoid obscuring the invention with unnecessary detail . in the present invention , an electromagnetic rfid tag is provided on a pill , with the rfid tag providing information about the medicament when polled by the rfid reader . antennas in the rfid tag and reader could be in different sizes and shapes , with the size of the tag antenna corresponding to the size of the pill , and the external reader fashioned in a manner to accommodate wearing by the patient on his or her body . in a preferred embodiment , a necklace / pendant is provided for the reader , as shown in fig1 . in alternative embodiments , the reader is clipped to the belt or a waistband . with such configuration a maximum achievable distance at which the reader can detect the presence of the rfid tag extends beyond the distance between the rfid tag inside the body and the external reader . in the present invention , spatial selectivity is possible as the region of the possible location of rfid tag is known , such as in regard to rfid tag localization , where measurements of the first - order spatial gradients of the magnetic field have been demonstrated . see , t . nara and s . ando , “ localization of rfid tags from measurement of complex gradients of electromagnetic fields ” , international workshop on networked sensing systems ( inss 2004 ), pp . 63 - 66 , 2004 . the differential signal was produced by oppositely wound coils . standard beamforming phased arrays techniques are not suitable for use in the external reader . the reason is that the performance of beamforming algorithms directly depends on the aperture of the array , and with the decreasing distance between array elements performance degrades , leading to the requirement of a large form factor of the external reader for extended range . a gradient flow method originates from localization of traveling waves . location of the source can be obtained as an estimation of the source direction through computation of the spatial gradients for the arrays with dimensions smaller than but comparable to the wavelength . in spatial gradient representation , time delays are converted into relative amplitudes of the time - differentiated source signals , if the dimensions of the array are within certain bounds . by computing the spatial gradients , the problem of estimating unknown time delays becomes a computationally less expensive problem of estimation of amplitude modulation , solved in standard least - square fashion . instead of localization , the gradient flow technique in the proposed spatially selective external reader is used to direct the magnetic energy into certain regions by generating spatial gradients using closely spaced antennas . the present invention monitors drug regimen compliance by tracking an rfid tag ( 120 ) affixed to a pill ( 110 ), i . e . ingestible pharmaceutical agent , via a wearable rfid reader ( 200 ), preferably configured as a harness ( 260 ) worn by a patient ( 305 ), as shown in fig1 . the rfid tag ( 120 ) includes information identifying the pharmaceutical agent ( 110 ) and such information is wirelessly transmitted to reader ( 200 ), which in turn provides the information , along with an identification of the patient wearing the reader ( 200 ), to an internet based central monitoring system ( 400 ), preferably immediately upon ingestion of the pharmaceutical agent ( 110 ). the central monitoring system ( 400 ) will , upon communication and confirmation of the ingestion , compare the received information to information stored in a database ( 410 ) to determine whether the patient is sufficiently compliant with a prescribed drug regimen . preferably , the database ( 410 ) will identify each of a plurality of harnesses respectively worn by a plurality of patients . moreover , if a patient ingests an rfid labeled pill that is not prescribed for that patient , or if the patient ingests an excessive number of rfid labeled pills , the central monitoring system ( 400 ) will provide an overdose alarm to a caregiver . in a preferred embodiment , an alarm is provided to a caregiver when the database is not updated at a predetermined interval , and the alarm will identify each particular patient who is not in compliance with that patient &# 39 ; s prescribed drug regimen . the caretaker will also have access to a report generated at regular intervals showing times that ingestion is detected for each patient among the plurality of patients . in a preferred embodiment , a plurality of antenna layers is provided on the rfid tag ( 120 ), with the layers separated by a plurality of coatings that sequentially dissolve during digestion . preferably the rfid reader ( 200 ) detects whether a first layer of the rfid tag ( 120 ) has dissolved , which typically occurs upon exposure to liquid when placed in the patient &# 39 ; s mouth . for purposes of fraud detection and to confirm proper ingestion , an alert is preferably provided if the first layer is detected as not being dissolved at the time of detection by the rfid reader ( 200 ), via an auxiliary antenna having a denser coating that dissolves further along the gastrointestinal tract . in a preferred embodiment of the present invention , the harness ( 260 ) positions the rfid reader ( 200 ) adjacent to the patient &# 39 ; s throat ( 310 ), and the rfid reader ( 200 ) is fixably secured to the harness ( 260 ). further , it is preferred that the harness ( 260 ) wirelessly communicates an alarm when unfastened from the neck of the patient ( 305 ). as an alternative to fixable securing harness ( 260 ), a second rfid tag can be incorporated into the wrist bracket that most hospitals provide upon admission , with the second rfid tag identifying the patient . such wrist brackets are unique and can not be effectively removed without destroying the bracelet . reader ( 200 ) would also poll the second rfid tag , and communicate the wrist mounted second rfid along with the identification of the ingested pill . the rfid reader is preferably uni - directional , directed toward the patient &# 39 ; s throat , to avoid a “ false positive ” that can arise if the patient dips the pill in water and then waives the pill near the reader , without ingesting , i . e . swallowing , the pill . while the invention has been shown and described with reference to certain exemplary embodiments of the present invention thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and equivalents thereof .