I’m sure you’ve noticed that your Messages alerts sound twice: once when you get the message, and again two minutes later. If this isn’t your cup of tea, there’s an easy way to change it. Repeat Alerts can be found, and changed, in the Settings app. You can choose to set repeat message alerts from Never all the way up to 10 times. It’s good to know that all alerts repeat in two-minute intervals. Here’s how to turn off repeat message notifications.
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Open Settings
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Tap Notifications
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Select Messages
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Scroll down to the bottom, and tap Repeat Alerts
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From here, you can choose Never
Now, you’ll receive a single notification for messages you receive
If you’re on the other end of the notification preference spectrum, you can also select twice, 3 Times, 5 Times, and 10 Times, with all alerts repeating in two-minute intervals.