RFBluetooth Active vs Passive Scanning : Key differences
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Introduction : Bluetooth scanning allows devices to discover nearby advertisers, with active and passive scanning offering different trade offs. Active scanning requests additional data for richer information, while passive scanning conserves power by listening only.
In Bluetooth Low Energy (BLE), scanning is the process by which a central device (like a smartphone) listens for advertising packets from peripheral devices like sensors or wearables.
Passive Scanning
- The scanner only listens to advertising packets.
- It does not send any packets back to the advertiser.
- The advertiser only sends its regular advertising data.
- Used when low power consumption is a priority and extra details are not needed.
Active Scanning
- The scanner listens to advertising packets and responds with a Scan Request (SCAN_REQ).
- The advertiser, upon receiving this, sends a Scan Response (SCAN_RSP) containing additional data.
- Allows the scanner to get more detailed information than what’s in the initial advertising packet.
- Consumes more power due to extra transmissions.
Difference between active and passive scanning
| Feature | Active Scanning | Passive Scanning |
|---|---|---|
| Interaction | Listens and Sends Scan Requests | Only listens |
| Extra information | Can receive additional data in scan response | Receives only advertising packet data |
| Power consumption | Higher | Lower due to no transmissions |
| Discovery speed | Faster | Slower |
| Use case | Quick device discovery with extra details | Low power background discovery, beacons |
| Security Exposure | Higher as scanner reveals its presence to advertiser | Lower due to less device visibility |
Conclusion: Choosing between active and passive scanning depends on the application’s priorities such as power efficiency or data richness. A balanced approach can yield both effective device discovery and extended battery life.
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