Yes, alarm sensors can be fit to uPVC window frames in the same way they are fitted to other types of windows.
As with all alarm systems, it is important that the alarm sensors are fitted professionally to ensure that they function correctly.
You should also speak to your installer when discussing your new window frames with them in order to confirm exactly how the sensors will be fitted. This ensures that the frames that are provided to you are suitable. Your installer will also be able to provide technical information about the frame that you can pass onto your security alarm fitter to prevent any problems arising when the sensors are applied.