Twilio started billing customers for Monitor Events on September 1st, 2015. There are specific charges for Events written, Events read via the API, and Events stored. For each of these three we have free tiers, the first 5000 Events written are free, the first 10,000 Events read via the API are free, and each Monitor Event is stored for free for the first 30 days. Most customers Monitor usage falls well below these free tiers. Please refer to our Monitor Events Pricing page and Audit Events pricing FAQ for more details.
Opting In and Out
Customers are automatically opted into Monitor, because your usage will fall well within Monitor’s free tiers when you start out. This gives you the opportunity to experience Monitor. Furthermore, as your usage approaches one of the free tiers, Twilio will send you an email notification (to the owner of the Account) informing you that your usage is approaching the free thresholds.
You may opt out of Monitor Events entirely, or opt into specific events that are of use to you via the Monitor Event Configuration Page. For example, if you need to keep track of every time a phone number changes you may use the Monitor Event Configuration to just select those events to be stored. You will not be charged for other events and other events will not be recorded on your behalf.