I have a prototype location tracker that costs <$4 to build. It can track any item's location every hour in urban areas for 30 days world wide (connects via wifi). Its smaller than a walnut. Would you use it? If so what for?
If it could work in rural areas, then cows... my uncle spends several days on horseback every year trying to round up his cows. If he could know exactly where the cows were it could save him days. If I’m stuck to urban areas, maybe look at dogs cats and carrier pigeons.