Intruder alarms are devices that alert the owners and the people in charge of security in any events of intrusion. Intruder alarms can take a variety of forms, from the simple household burglar alarms to the complex and sophisticated Intrusion Detection Systems (IDS) used in securing enterprise level computer systems.

The main importance of intrusion alarms is that it lets the people concerned with security to be informed of any intrusion events. By being informed of such events, these people can quickly react to prevent or even mitigate any loss or damages resulting from such intrusion. The police can quickly dispatch policemen to a particular household should there be an intrusion, and in the context of computer systems security, the systems administrator can quickly patch out the vulnerabilities in their computer systems.

One of the most common forms of intruder alarms is the household burglar alarm. The most common implementation of such intruder alarms is much like a trip wire. If a burglar trespasses when the burglar alarm is engaged, it creates a loud noise to call the attention of the house owner and to scare away the burglar. In some developed countries like the United States and Canada, these household burglar alarms are connected to the police such that the police can quickly dispatch people to look into the situation.

Intruder alarms can also be sophisticated. Like in the case of computer systems, Intrusion Detection Systems (IDS), devices or software that primarily used in a computer system to monitor network and system activities to detect malicious traffic or activities that violate the organization's rules and policies. These systems have the ability to automatically generate reports to give the people in charge of the system an overview of the intrusion such that an appropriate response to the incident can be done. In addition to that, these IDSes can also have the ability to automatically react and trigger security measures automatically to counter an imminent threat.

Although intruder alarms can be very helpful when securing something, one has to be very careful when setting up and configuring these devices. When an intrusion alarm keep on detecting false positives it may be deemed as "untrustworthy" making alarms from that device being ignored because mobilizing resources to respond to an intrusion, especially in sophisticated intrusion detection systems can prove costly.

All in all, intruder alarms when set up and configured properly can be a very useful addition when securing something. Being able to know when there is an event of intrusion can prove to be very useful to generate an effective response to a security incident.