There are limits by notification type. Each subscription plan comes with a maximum number of notifications that will be sent by your account for each type of notification. There are three (3) types of notifications.
checkSMS (Text Messages)
Email notifications are unlimited but there are limits to the number of SMS Text messages and Voice Calls that will be sent on each month's monitoring cycle. Each limit is described in detail in the monthly subscription plan. Check the Pricing page for the standard plans and their limits.
Additionally, there are Bundled Options that allow you to increase the number of Notifications that you can receive for SMS Text Messages and Voice Calling.