A Nearby Notification shows when a user pulls their screen down to open their Android phone, or open their notification shade. It looks like a regular notification, but it's only visible as long as the phone is within reach of the Eddystone beacon that broadcasts the message.
Just like a radio, the Bluetooth beacon can broadcast one notification at a time. But it is possible to send out different notifications on different times. And different notifications for different languages.
You need a beacon that supports the Eddystone UID protocol. You can manage these beacons with the Google Beacon Platform, or use the Landing Framework to let multiple users control their beacons with one Google Platform account (yours). This is easier, because then you are the only one who needs to set up a platform key and SSL connection. Which are required to broadcast a Nearby Notification.
Your customers can then add beacons and notifications right away without and technical knowledge. On top of this, you can easily create content with the Landing Framework to show when a user opens a notification. Analytics included!
A phone will not ring or vibrate, as it's not a text message or call. It is seen when the user pulls their screen down to open their phone. An avarage user does this 40+ times a day.
Nearby Notifications will only show up on Android phones, from version 4.4 and up. This is a huge market share.
This is not considered spam, because Nearby Notifications are a feature in the Android Operating System. The first time a user encounters a beacon they are asked if they wish to see the message the device is trying to send them. Most people allow this, and now they have opted in for future messages from all devices. A user can turn this off at any time, so it's up to you to give them a good reason to stay connected.