It works because the Bluetooth FOB alerts you when you move a certain distance from a tagged item.

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Should a suicide be assisted when a patient is a certain distance from death, or when he has simply given up hope?

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The council is committed to providing free transport for children with SEN and mainstream pupils who live a certain distance from their school.

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Telling the world how it ought to be does, after all, require a certain distance from those messy things like details and the opinions of others.

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For example, the chips used to protect your jeans against theft in a supermarket use active RFID - the chip can be detected and tracked from a certain distance.

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The idea: Passengers use an app to request a ride, the request goes to all participating cabbies within a certain distance and the driver who responds first gets the fare.

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Black holes are notoriously difficult to study, since so much in astronomy depends on the detection of light - and within a certain distance from a black hole, even that cannot escape.

BBC: First glimpse of a black hole's spin

Radar embedded in the front of the Fusion sweeps the road ahead and when the adaptive cruise control is activated the car automatically slows down as it approaches another vehicle within a certain distance and then speeds up when the gap widens.

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As would be expected, you're supposed to stand relatively center on the TV, and at a certain optimal distance.

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He has a certain amount of intellectual and emotional distance from the banking world he inhabits.

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