# Triggers

A trigger is a recording a sensor makes when shaking crosses its threshold. It keeps the waveform from before the threshold was crossed until the shaking stopped. Sensors on the [Structural plan](/modules/structural-health-monitoring) record triggers by default; any sensor can be [switched to triggered recording](/dashboard/sensors/recording-mode).

Triggers are not earthquake detections. Each one is the shaking at one sensor, whatever caused it: an earthquake, machinery, traffic, construction, or someone bumping the sensor.

## The Triggers page

Open **Triggers** in the sidebar.

![Triggers page in Grillo Cloud](/img/screenshots/triggers-list.png)

| Column | Meaning |
|---|---|
| Time | When the shaking peaked |
| Sensor | Station code and location name |
| Duration | From the start of the recording to its end |
| Horizontal PGA | Peak ground acceleration on the horizontal axes combined, in mg and %g |
| Vertical PGA | Peak ground acceleration on the vertical axis |
| Vertical PGV | Peak ground velocity on the vertical axis, from the geophone |
| Dominant frequency | The frequency with the most energy at the peak |
| Status | **recording…** while the sensor is still uploading, then **complete** |

Select **Time** or **Horizontal PGA** to sort. Use **Sensor** to show one sensor's triggers, and **Date** to choose a range in UTC. The page shows 50 triggers at a time and refreshes every minute.

Select a trigger to open its details.

### Units

- **mg** is thousandths of the acceleration of gravity: 1000 mg = 1 g = 9.81 m/s².
- **%g** is the same value as a percentage of gravity: 100 mg = 10 %g.
- Peaks are measured after filtering to 0.5–25 Hz, which removes the sensor's offset and slow drift.

## Trigger details

![Trigger details with waveforms in Grillo Cloud](/img/screenshots/trigger-detail.png)

The details show the sensor, the start, end, duration, and peak time, and the peaks:

- **Horizontal PGA**, and the PGA on each axis: **East (HNE)**, **North (HNN)**, and **Vertical (HNZ)**
- **Vertical PGV** in mm/s, for sensors with a calibrated geophone
- **Geophone peak (EHZ)** in counts
- **Dominant frequency**

While a trigger is still recording, its values update every 15 seconds as data arrives.

**Email alert** shows whether an alert was sent for this trigger, and if not, why. See [Trigger Alerts](/dashboard/alerts#on-the-trigger-page).

### Waveforms

The **Waveform** section has one chart per channel: **East**, **North**, and **Vertical** acceleration in mg, and the **Geophone** in counts. The time axis is seconds from the peak, which is marked by an orange line. Dashed lines labelled **Start** and **End** mark the trigger window, and the charts include 5 seconds either side. Shaded bands mark gaps in the data.

A trigger longer than 5 minutes shows the 5 minutes around its peak.

Select **Open in waveform archive** to look at the same interval in the [waveform archive](/dashboard/data/waveforms). On plans that include waveform download, **Download (miniSEED + CSV)** saves the trigger window as a [zip file](/dashboard/data/waveforms#download-data).

## Recent triggers for a sensor

Each sensor's details list its 8 most recent triggers. Select **View all triggers** to open the Triggers page filtered to that sensor.

## When a trigger appears

A trigger appears in Grillo Cloud once the sensor starts uploading, usually within a minute of the shaking. It stays **recording…** while the sensor uploads its pre-event buffer and the shaking, and becomes **complete** after the sensor stops sending.

- A sensor that keeps shaking for a long time is split into triggers of at most 15 minutes.
- If a sensor's data stops for more than 10 seconds in the middle of a recording, what follows is a new trigger.

## If no triggers appear

1. Confirm the sensor is [online](/dashboard/sensors/sensor-status) and its details show **Triggered**.
2. Check its threshold. A threshold above the site's normal vibration records nothing until real shaking arrives. To test a sensor, tap the side of the enclosure firmly; the trigger count in its details goes up.
3. Check the **Date** range and the **Sensor** filter, then select refresh.

If a sensor records too many triggers, raise its threshold. See [Recording Mode and Thresholds](/dashboard/sensors/recording-mode#choose-a-threshold).

## Get triggers by API

Triggers are also available from the [Data API](/dashboard/data/api#triggers).