It is important to note that the software is installed on the phone and not the SIM card. As soon as the target changes the SIM, you will get a SIM change notification alert on your phone. To enable this feature, you need to log in to your online account and head over to Control Centre tab > Bugging Controls > Set Monitor Number. Then enter your own mobile phone number in the international format (e.g. +1XXXXXXXXX). Once you have upgraded these changes, you will always receive a SMS notification whenever there is a SIM change on the target device. As the SMS would be sent from the new number of the target device itself, you can easily note the number, without going through any hassle.