Defining the customer's or end user's needs is the first and most important step of the product development process. Vague product specifications are a hotbed for misapprehension, leaving the development process prone to errors.
For a thorough specification it is paramount to pin down the feature set that the device in question will possess since these features will form the frame of the project. To define these features we look at the customer's wishes regarding the communication protocols, cyber security criterea, display type and size, number of buttons, input- and output ports and -types, possible wall mounting options, moving parts, use cases in which the device will have to perform, possible unintended use cases. There are instances of variations of a single product where getting rid of a few unneded features makes the 'offspring' a much more affordable but still uncompromised device for some cases.
Towards the end of the development process certified third party bodies test the end product compliance with the features defined at this phase.