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Farmers in the US who want to know when their cows become fertile can glue a
special patch called HeatWatch to their tails. Inside the patch is a
piezoelectric sensor and a tiny radio with a 400-metre range. Farmers normally
know that a cow is in oestrus when other cows in the herd try to mount her. When
a cow receives unwelcome attention from other cows the piezoelectric pressure
sensor is triggered and a radio signal is sent. Cows are only in oestrus for
10–12 hours each month. So the patch will be a boon to farmers, telling
them the optimum time to artificially inseminate the cows.