The smart-me Realtime (Webhooks) API allows you to subscribe to new data of a device. You can subscripe to a single device or to all devices of a user. When a device sends new data to the cloud, a webhook sends this data as a POST request to a preconfigured URL.
A single device can send it's data up to once a second. If you subscripe for a larger number of devices get sure that your API can handle this load.