An exit monitor is a tool used in digital marketing to detect when a visitor is about to leave a website. When a visitor's mouse moves towards the close button or address bar, an exit monitor triggers a pop-up or overlay, presenting a final opportunity to capture the visitor's attention. This can be a subscription form, special offer, or another call-to-action (CTA). In the context of email marketing, it is often used to capture email addresses before the visitor exits, thereby growing your email list.