▁E AS ▁covers , ▁which ▁are ▁made ▁of ▁dur able ▁vin yl , ▁offer ▁cost - effect ive ▁means ▁of ▁adding ▁a ▁market ing ▁tool ▁at ▁every ▁entrance ▁to ▁a ▁store ; ▁they ▁are ▁also ▁custom - man ufact ured ▁to ▁fit ▁any ▁ped est al ▁and ▁can ▁be ▁printed ▁to ▁highlight ▁specific ▁br ands ▁or ▁season al ▁prom ot ions . ▁They ▁do ▁not ▁inter f ere ▁with ▁the ▁performance ▁of ▁the ▁E AS ▁systems ▁and ▁are ▁easily ▁clean ed ▁or ▁changed . ▁Some ▁shop l if ters ▁may ▁employ ▁jam mer ▁devices ▁to ▁prevent ▁E AS ▁tags ▁from ▁trigger ing , ▁or ▁magnet s ▁to ▁remove ▁the ▁tags . ▁St ores ▁may ▁employ ▁technology ▁to ▁detect ▁j amm ers ▁and ▁magnet s . ▁ ▁Radio - fre quency ▁identification ▁( R F ID ) ▁is ▁an ▁anti - employee - the ft ▁and ▁anti - shop l ifting ▁technology ▁used ▁in ▁ret ail ers ▁such ▁as ▁Wal mart , ▁which ▁already ▁heavily ▁use ▁R F ID ▁technology ▁for ▁invent ory ▁purposes . ▁If ▁a ▁product ▁with ▁an ▁active ▁R F ID ▁tag ▁passes ▁the ▁exit ▁sc ann ers ▁at ▁a ▁Wal mart ▁out let , ▁not ▁only ▁does ▁it ▁set ▁off ▁an ▁alarm , ▁but ▁it ▁also ▁tells ▁security ▁personnel ▁exactly ▁what ▁product ▁to ▁look ▁for ▁in ▁the ▁sho pper ' s ▁cart . ▁ ▁Add - on ▁metal ▁det ector ▁systems ▁will ▁be ▁used ▁in ▁some ▁stores ▁with ▁electronic ▁article ▁surve ill ance ▁which ▁sense ▁met all ic ▁surfaces .