Which device does NOT emit electromagnetic radiation?

Calculators do not emit electromagnetic radiation because they primarily operate using low-power electronic components that do not generate or transmit radio waves or other forms of electromagnetic radiation. They use simple digital circuits and typically do not require wireless communication, which is necessary for the emission of electromagnetic radiation.

In contrast, smartphones, microwave ovens, and wireless routers all function by emitting electromagnetic radiation. Smartphones and wireless routers use radio waves for communication, while microwave ovens utilize microwaves to heat food, both of which are forms of electromagnetic radiation. Therefore, the calculator stands out as the only device in the list that does not engage in such emissions, which is why it is the correct answer.