Many hotels experience little or no mobile signal inside the building, even when they are located in big cities. Walls are usually thick stone, or mass concrete. Windows are usually triple glazed, and the doors are often fire-proof doors which contain a layer of metal within. All this prevents mobile signal from entering the rooms. Hotels are often located within one hundred metres of the operator’s tower but still experience poor signal inside. Customers and staff may have to stand beside the window to get a good signal. This is far from ideal.