vei сказал(а):
push notification can be useful, like when they are pushed rapidly and users accidentally click it when it appears over link/button they meant to click on page instead.
you could simulate fake windows warnings, but if you have the ability to insert javascript already, there are better options to pursue depending on the website.
but you question is vague, so it is hard to answer directly without knowing more information. there are notifications via malicious mobile calendar add-ons, notifications from browser extensions, notification from maldvertisments, etc. please be more clear about your question.