| 摘要 |
A method of estimating the number of people (36, 38, 40) within a predetermined range of a particular location, which method comprises the steps of:- <SL> <LI>(a) using an antenna means (18) to listen for electromagnetic communication signals indicative of the presence of one or more remote electronic data communication device (24, 26, 28) likely to be carried about the person of one or more of said people (36, 38, 40); and <LI>(b) providing an electronic output signal from said antenna means (18) representative of said presence; </SL> ```which electronic output signal facilitates estimation of the number of people (36, 38, 40) within said predetermined range.
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