A system comprising a smoking substitute device and a mobile device, wherein the mobile device is wirelessly connected to the smoking substitute device; wherein the smoking substitute device is configured to generate an aerosol from an aerosol forming substrate, the smoking substitute device comprising an audio interface; wherein the smoking substitute device is configured to perform a speech control function that includes: recognising words spoken by a user in an audio signal obtained by the audio interface; using a natural language processing model stored on and configured to be run by the smoking substitute device to analyse the recognised words spoken by the user; if a confidence level associated with a command recognised by the natural language processing model is less than a predetermined threshold value, perform a verification function to verify the command intended to be executed by the user; and controlling an operation of the smoking substitute device based on the analysis of the recognised words spoken by the user; wherein the smoking substitute device is configured to prevent the audio signal obtained by the audio interface from being communicated from the device to the mobile device; and wherein the verification function includes: using the natural language processing model to generate a sequence of words asking the user to verify whether the recognised command should be implemented; using an output device of the mobile device to produce an output which provides the sequence of words to the user; and if, in response to the output, the user verifies that they want to implement the recognised command, controlling operation of the smoking substitute device to implement the recognised command. recognising words spoken by a user in an audio signal obtained by the audio interface; using a natural language processing model stored on and configured to be run by the smoking substitute device to analyse the recognised words spoken by the user; if a confidence level associated with a command recognised by the natural language processing model is less than a predetermined threshold value, perform a verification function to verify the command intended to be executed by the user; and controlling an operation of the smoking substitute device based on the analysis of the recognised words spoken by the user; wherein the smoking substitute device is configured to prevent the audio signal obtained by the audio interface from being communicated from the device to the mobile device; and wherein the verification function includes: using the natural language processing model to generate a sequence of words asking the user to verify whether the recognised command should be implemented; using an output device of the mobile device to produce an output which provides the sequence of words to the user; and if, in response to the output, the user verifies that they want to implement the recognised command, controlling operation of the smoking substitute device to implement the recognised command. using the natural language processing model to generate a sequence of words asking the user to verify whether the recognised command should be implemented; using an output device of the mobile device to produce an output which provides the sequence of words to the user; and if, in response to the output, the user verifies that they want to implement the recognised command, controlling operation of the smoking substitute device to implement the recognised command.