Illegal immigrants planning to cross the desert and enter the US on foot are to be given hand-held satellite devices by the Mexican authorities to ensure they arrive safely. Those who get lost or fall sick during the dangerous four-day crossing will be able to activate the device, to alert frontier police on both sides of the border. The satellite tracking service will require would-be illegals to register their intentions before setting off — a paradoxical move, given that secrecy is necessary for success — but Mexican authorities are predicting that about 200,000 devices will be handed out when the...