An Intrusion Detection System (IDS) is the correct answer because it is specifically designed for the passive monitoring of network traffic and alerting when suspicious activities or known threats are detected. Unlike an Intrusion Prevention System (IPS), an IDS does not actively block potential threats; it instead focuses on the detection aspect and relies on others to respond to the threats it identifies. A Firewall controls incoming and outgoing network traffic based on an applied rule set and is not designed solely for the detection of threats. A Load balancer distributes network or application traffic across a number of servers to optimize resource use, maximize throughput, reduce response time, and avoid overload on any one server.