Surveillance can operate as an agentless or agent-based product.
A web-based user interface (web client) provides access, along with other tools.
As an agentless product, Surveillance is installed on a machine and can monitor databases remotely. The Surveillance Server agents just run on the same machine as the client or web tier. This is how Surveillance Express Edition works, and is a great way to trial the product.
Surveillance is more commonly deployed as an agent-based product. The Surveillance Server agents, or SAM, reside on each server that runs a database. This provides the most reliable, efficient, and extensive monitoring possible. You can also have databases being monitored remotely, creating a hybrid agent-based and agentless deployment.