Create an Organizations SCP deny policy that has a condition that the aws:RequestedRegion property does not match a list of all US Regions. Include an exception in the policy for global services. Attach the policy to the root of the organization.

Configure AWS CloudTrail to send logs to Amazon CloudWatch Logs. Enable CloudTrail for all Regions. Use a CloudWatch Logs metric filter to create a metric in non-US Regions. Configure a CloudWatch alarm to send an alert if the metric is greater than 0.

Use an AWS Lambda function that checks for AWS service activity. Deploy the Lambda function to all Regions. Write an Amazon EventBridge rule that runs the Lambda function every hour. Configure the rule to send an alert if the Lambda function finds any activity in a non-US Region.

Use an AWS Lambda function to query Amazon Inspector to look for service activity in non-US Regions. Configure the Lambda function to send alerts if Amazon Inspector finds any activity.

Create an Organizations SCP allow policy that has a condition that the aws:RequestedRegion property matches a list of all US Regions. Include an exception in the policy for global services. Attach the policy to the root of the organization.