as seen in fig3 a , 3 b and 5 , the conventional tire pressure monitoring system 1 may be modified by algorithm logic 10 , 100 that detects and reacts to an interfering signal 5 , 7 other than that of wireless tire pressure signals ( tps ) associated with an in - use tire 4 a - 4 d . as such , any sensor data / wireless signal that appears to be foreign in nature to the algorithm 10 , 100 , such as , for example , the signals 5 , 7 , may be screened and rejected to ensure proper operation of the inventive systems 1 a , 1 b . the algorithm logic 10 , 100 may , for example , be coded in the receiver &# 39 ; s microprocessor . referring initially to fig3 a , a first algorithm 10 for screening and rejecting an interfering signal 5 is illustrated according to an embodiment . the algorithm 10 is started at step i . upon keying the vehicle , v . although the following description is related to an active operation of the vehicle , v , ( i . e ., when the vehicle , v , is keyed ), it will be appreciated that the algorithm 10 analyzes received tire pressure signals upon powering the receiver 2 a with battery voltage . accordingly , although the following description relates to a keying of the vehicle , v , tire pressure signals may be received and analyzed when the vehicle is in a keyed - off state . when an interfering signal 5 is not detected by the algorithm 10 , normal operation of the system 1 a is carried out in a continuous looping of steps 14 - 28 . however , if an interfering signal 5 is imparted to the receiver 2 a in an intentional or unintentional manner , normal operation of the system 1 a is ceased at step 24 , which causes the algorithm 10 to lockout the corrupting , interfering signal 5 for a determined period of time at steps 30 - 36 ( fig3 b ). during normal operation of the algorithm 10 , the wireless tire pressure signals 3 a - 3 d are individually processed by the microprocessor , but , for purposes of explanation in describing the flowchart shown in fig3 a , the four wireless tire pressure signals 3 a - 3 d are examined at the same time . if simultaneous examination of the wireless tire pressure signals 3 a - 3 d is desired , the electronics and / or software of the system 1 a may be modified accordingly . referring now to step 12 , upper and lower limits of an average signal strength envelope , which are used for comparison in the conditional test at step 24 , are set after keying the vehicle , v , at step i . the upper and lower limits that are set in step 12 may be learned , dynamic values ( i . e ., from the function described in steps 26 and 28 ). essentially , the upper and lower limits are saved in memory from a previous operation of the vehicle , v . as such , the upper and lower limits may be recalled at step 12 when the vehicle , v , is keyed in a subsequent operation . because the upper and lower limits may vary throughout the life of the vehicle , v , the algorithm 10 will operate more efficiently with recalled , learned values at step 12 rather than re - setting the algorithm 10 to operate with a broader signal strength range defined by preset upper and lower limits at the outset of keying the vehicle , v . however , if desired , pre - programmed upper and lower limit calibration may be used at the outset of the algorithm 10 in step 12 rather than applying the use of learned values from steps 26 and 28 . then , at step 14 , the wireless tire pressure signals 3 a - 3 d are received by the receiver 2 a . each wireless tire pressure signal 3 a - 3 d is identified by the algorithm 10 with a specified identification ( id ) that is validated at step 16 . because surrounding vehicles may be also transmitting their own tire pressure signal ids for their own tire pressure monitoring systems , such unintentionally - received ids identified at step 16 are simply ignored , and the algorithm 10 is looped back to step 14 . however , if an intentional or unintentional interfering signal 5 is matched with a corrupting id that passes the validation test at step 16 , the interfering signal 5 associated with the corrupting id is screened in a subsequent step identified at reference numeral 24 . accordingly , if such a condition occurs , the algorithm 10 may process the interfering signal 5 with the expected tire pressure signals 3 a - 3 d as follows starting with step 18 . at step 18 , the algorithm 10 tracks the number of signal readings for each tire pressure signal id during a sampling period to determine if enough readings have been received so as to average the signal strength in step 26 . as such , if the expected number of signal readings during the sampling period were not received , the algorithm logic at step 20 is looped back to step 14 . however , if the expected number of signal readings were received at step 20 , the algorithm is further advanced to step 22 . in step 22 , the algorithm measures the signal strength for wireless tire pressure signals 3 a - 3 d associated with their respective ids . then , at step 24 , the second conditional test compares the measured signal strength for each tire pressure signal 3 a - 3 d associated with the expected ids against the dynamically - adjusted signal strength envelope . if the measured signal strength is within or close to the signal strength range defined by the upper and lower limits , the algorithm 10 is advanced to step 26 . alternatively , if the measured signal strength is not close to or within the signal strength range , the interfering signal 5 associated with the expected id may be detected and locked out by being advanced to step 30 from step 24 . because the signal strength envelope is dynamically adjusted over the life of the vehicle , v , it is increasingly difficult for an interfering signal 5 to tamper with the operation of the system 1 a . the dynamic adjustment of the signal strength envelope is performed at steps 26 and 28 , which is subsequent to the conditional test at step 24 if no lock - out period has occurred for the screened tire pressure signals . at step 26 , the measured signal strengths from step 22 are averaged to calculate an averaged signal strength value . then , at step 28 , the envelope limits are dynamically updated in view of the averaged signal strength value calculated in step 26 . according to one embodiment of the invention , step 28 may include a first calculation to determine the percentage difference of the averaged value against the upper and lower limit values . then , the calculated percent difference is added or subtracted to the upper and lower limits . it will be appreciated that the above - described update at step 28 may be carried out by using other designs . for example , after the average value is determined , the averaged value may be compared against the upper and lower limits , and then the average value may be swapped with one of the upper and lower limits . accordingly , the illustrated algorithm logic 10 may screen and lockout an interfering signal 5 according to the conditional test at step 24 . as such , if an interfering signal 5 is imparted onto the system 1 a , the algorithm logic 10 maintains proper operation of the system 1 a . as shown in fig3 b , the lockout may occur for any desirable period of time and may be incremented accordingly at step 32 . when the algorithm 10 has determined that the lockout period has ended at step 34 , the failed tire pressure signal id ( s ) is unlocked at step 36 and the algorithm logic 10 returns to the beginning of the loop at step 14 . thus , even if the interfering signal 5 maintains its presence after being unlocked at step 36 , the interfering signal 5 associated with an expected id may be continuously locked out until it wanes . although only one conditional test is shown at step 24 , any desirable numbers of tests may be implemented in the algorithm 10 in any desirable scheme . additionally , such additional conditional tests may be dynamic in nature as in step 24 , and may be adjusted in a similar fashion as shown in steps 26 - 28 when the upper and lower limits of the average signal strength changes during normal operation of the algorithm 10 . as such , because the conditional tests may be dynamic , the algorithm 10 lends itself to a constantly changing defense mechanism that would make it increasingly difficult for an intentional or unintentional interfering signal attack to be successfully executed . referring to fig4 , another embodiment of the invention is directed to a situation that addresses the potential for reception of an interfering signal originating from within the vehicle , v . as illustrated , a spare tire 4 e transmits a signal 7 including a tire pressure signal id such that the receiver 2 b looks for five wireless tire pressure signals 3 a - 3 d , and 7 associated with five tire pressure signal ids rather than four wireless tire pressure signals 3 a - 3 d associated with four tire pressure signal ids as in the embodiment described in fig2 - 3b . accordingly , the system 1 b permits itself to monitor if one of the in - use tires 4 a - 4 d becomes flat and is swapped with the spare tire 4 e . if the swap is not properly recognized by the receiver 2 b , the previously - designated in - use tire , which may be reconfigured to a stationary state , may result in the unintentional sending of a false signal to the receiver 2 b from within the vehicle , v . as seen in fig5 , algorithm logic 100 according to another embodiment of the invention is provided for the system 1 b such that the receiver 2 b automatically updates in - use and spare tire location . as similarly described above with respect to fig3 a and 3b , the system 1 b is started at step a . then , at step 102 , wireless tire pressure signals 3 a - 3 d and 7 relating to tire pressure signal ids of the in - use tires 4 a - 4 d and spare tire 4 e are sent to the receiver 2 b . at step 104 , the algorithm logic 100 checks to see if the wireless tire pressure signal 7 relating to the spare tire 4 e is in a stationary state . the stationary state of any of the tires 4 a - 4 e may be based upon any desirable transmission rate or coded message content . if it is determined that the spare tire 4 e is in a stationary state , the algorithm logic 100 is advanced to steps 106 and 108 where flags relating to an unloaded and loaded state identifier tags are maintained for the spare and in - use tires 4 a - 4 e . after steps 106 and 108 are executed , the algorithm logic 100 is returned to the beginning of the loop at step a . if the receiver 2 b discovers that the spare tire 4 e has been swapped with an in - use tire 4 a - 4 d , step 104 is advanced to step 110 . for the algorithm logic 100 to permit advancement to step 110 , it must be determined at step 104 that the spare tire 4 e is no longer in a stationary state ( i . e ., the spare tire 4 e is in a rotational state ). if so , the spare tire 4 e is flagged with a loaded state identifier at step 110 . then , at step 112 , the algorithm logic 100 determines which tire 4 a - 4 d is no longer under an in - use condition ( i . e ., the determined tire 4 a - 4 d is in a stationary state ). at step 114 , upon determining which tire 4 a - 4 d is in the stationary state at step 112 , the determined tire 4 a - 4 d is flagged with an unloaded state identifier tag . then , at step 116 , the algorithm logic 100 swaps the spare tire pressure signal id with the in - use tire pressure signal id . after the ids are properly swapped , the algorithm logic 100 is returned to the beginning of the loop at step a . accordingly , both embodiments of the invention illustrated in fig2 - 5 provide a modification to conventional tire pressure monitoring systems such that the wireless in - use tire signals 3 a - 3 d are secured by the algorithm logic 10 , 100 without costly changes , such as signal encryption . thus , an inexpensive method is provided and the tire pressure signal 3 a - 3 d data may be easily maintained by the receiver 2 a , 2 b . the present invention has been described with reference to certain exemplary embodiments thereof . however , it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the exemplary embodiments described above . this may be done without departing from the spirit of the invention . the exemplary embodiments are merely illustrative and should not be considered restrictive in any way . the scope of the invention is defined by the appended claims and their equivalents , rather than by the preceding description .