RF Wireless World

Browse articles, tutorials, tools, and vendors.

Bluetooth Notifications vs Indications: Key Differences

By RF Wireless Expert Team

As defined in Attribute Protocol (ATT) and Generic Attribute Profile (GATT) in the Bluetooth Core Specification, Notifications and Indications are two methods a Bluetooth device uses to send data asynchronously.

Normally, a GATT Client must send a “Read Request” to a GATT Server to get data. However, constantly polling for data wastes battery and bandwidth. To solve this, the specification allows the GATT Server to push data to the Client the moment the data changes.

While both Notifications and Indications serve this “push” purpose, they differ fundamentally in acknowledgment and reliability.

1. BLE Notifications

  • When a characteristic’s value changes on the GATT Server (e.g. a heart rate monitor detects a new heartbeat), the server immediately transmits a Notification containing the new data to the GATT Client (e.g., a smartphone).

  • Notifications are unacknowledged at the ATT layer. The server sends the data packet and assumes it arrived. It does not ask the client for a receipt, nor does the client send one.

  • Pros & Cons: Because there is no waiting for a confirmation message to travel back over the air, Notifications are very fast and highly power efficient. They are ideal for rapid streams of data where missing a single packet occasionally is not a critical failure.

2. BLE Indications

  • Similar to a notification, the GATT Server pushes an Indication containing the new data to the GATT Client.

  • Indications are acknowledged at the ATT layer. When the Client receives an Indication, it is strictly required by the protocol to send an ATT Confirmation message back to the Server. The Server can not send another Indication until it receives this confirmation for the previous one.

  • Pros & Cons: Because of the mandatory confirmation handshake, Indications are highly reliable at the application layer and server absolutely knows the client application received the data. However, this round trip handshake makes Indications slower, consumes more bandwidth and uses more battery power.

How are they turned on?

Neither Notifications nor Indications happen automatically. To save power, they are turned off by default. The GATT Client must explicitly tell the GATT Server to turn them on by writing to a specific metadata switch attached to the characteristic, known as the Client Characteristic Configuration Descriptor (CCCD).

Summary Comparison Table

FeatureGATT NotificationGATT Indication
Primary ActionServer pushes data to Client asynchronously.Server pushes data to Client asynchronously.
Application AcknowledgmentNo. The Client does not send an ATT confirmation.Yes. The Client must send an ATT Confirmation back to the Server.
Speed & ThroughputFast. Multiple notifications can be streamed rapidly.Slower. The Server must wait for a confirmation before sending the next indication.
Reliability (ATT Layer)Lower. If the packet is dropped at the application layer, the Server won’t know. (Note: The Link Layer still handles basic radio-level retries).High. Guaranteed delivery to the application layer; Server knows if the data arrived.
Power ConsumptionLow. Less radio-on time required.Higher. Requires transmitting and receiving for the handshake.
Typical Use CaseStreaming real-time sensor data (e.g., continuous Heart Rate, audio levels, live temperature).Sending critical state changes or alerts (e.g., “Battery Low”, “Device Error”, “Door Unlocked”).

References & Further Reading

  1. Bluetooth SIG : Bluetooth Core Specification Version 6.3, May 5, 2026.
  2. Bluetooth SIG : Bluetooth Technology Overview

Continue Learning Bluetooth Basic Concepts

Continue Learning Bluetooth Technology

Compare Bluetooth With Other Technologies

Keep Reading

Related Posts