Is it possible to create a vb.net or C # app to send notifications to mobile using bluetooth without any mobile app?
Not. It won't work.
APNS
GCM
https://developer.android.com/google/gcm/gcm.html
Push notifications should be migrated from Apple or Google's notification frameworks.
IOS has local notifications that your app can trigger based on your conditions, but as far as I know, when bluetooth connects, your app should be running and listening for bluetooth changes.
If your app goes into the background and is reworked, it won't be able to know when Bluetooth is connected, let alone trigger your logic to send notifications.
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No, It is Immpossible. Your title asks for "no mobile app". The mobile app on the device is what gets notified. You create a notification on the server (as shown in @ Lee's explanation) and your application decides whether to show it to the user or process the data behind the scenes.
Assuming we're neglecting the no mobile app part, you can do something similar with iBeacons. Department stores use them for targeted notifications in their app. You walk a specific counter with an iBeacon and your app shows a notification that this section is 20%.
Alternatively, you can in some way also use a service like Twilio that you can receive from a TEXT / MMS (notification) to someone based on a specific trigger that you define. However, this will require that you already have a phone number and some in order to determine that they are in your region.
In general, being able to notify people in the immediate vicinity who have not yet done something to subscribe (for example, download an app, provide contact information) is simple spam.
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