## Common ground
All options describe wearable electronic devices used for monitoring heart activity via chest straps.
## Options at a glance
**9029.20 – Heart rate counter**
- **Defining trait:** The device independently counts and displays heartbeats.
- **Typical examples:** Chest strap that shows real-time BPM on its screen.
- **Best fit when:** The device computes and reports heart rate without needing another device.
**9029.90 – Signal transmitter (no counting)**
- **Defining trait:** Transmits raw heartbeat signals but does not count beats.
- **Typical examples:** NuMetrex chest strap sending data to a separate tachometer.
- **Best fit when:** The device only sends signals to another device for processing.
**9031.80 – Multi-function tracker**
- **Defining trait:** Tracks heart rate plus other metrics (steps, sleep, calories) using motion sensors.
- **Typical examples:** Fitness tracker with chest strap that uses accelerometer.
- **Best fit when:** The device combines heart rate sensing with movement tracking and multiple health metrics.
**9031.90 – Signal transmitter to external device**
- **Defining trait:** Sends heartbeat signals to a smartphone, watch, or other instrument for measurement.
- **Typical examples:** Chest strap syncing with a smartphone app or bike computer.
- **Best fit when:** The device transmits data but relies on another device to analyze or display it.
## Key differences
| Feature | 9029.20 | 9029.90 | 9031.80 | 9031.90 |
|-----------------------|---------------|---------------|---------------------|---------------------|
| Counts heartbeats? | Yes | No | Yes (with motion) | No |
| Sends raw signal? | No | Yes | No (processed) | Yes |
| Multi-metric tracking?| No | No | Yes | No |
| Requires external device? | No | Yes | Optional | Yes |
## How to choose
- Does the device display heart rate on its own? → 9029.20
- Does it send raw heartbeat data but not count beats? → 9029.90 or 9031.90
- Does it track steps, sleep, or calories using motion sensors? → 9031.80
- Is it designed to work with a smartphone, watch, or bike computer? → 9031.90
## Overlaps & pitfalls
- **Overlap:** 9029.90 and 9031.90 both transmit signals; the difference is whether the device is standalone (9029.90) or part of a broader tracking system (9031.90).
- **Pitfall:** If a chest strap counts heart rate *and* sends data, prioritize based on **main function**: counting → 9029.20; transmitting → 9031.90.
- **Unclear priority:** When both signal transmission and multi-metric tracking apply, use the device’s primary purpose to decide