You can silence individual device alerts from the Device Manager by clicking actions next to the device and silencing for the desired period.
To silence multiple devices, click the checkbox next to each device you wish to silence and then click the blue actions label at the top of the table, and select the alert silence for the period you wish.
If you wish to silence devices for more than 3 hours, You can use the API. For information on how to do this, checkout https://wiki.dotcom-monitor.com/programming-interfaces/disable-alerts-for-a-device/.
Before you can use the API, you must notify support what IP addresses to allow API access from.