Detecting the IP address of a smart plug can be done using several methods, depending on your network setup and the smart plug's configuration:

1. Router Interface: Access your router's admin interface via a web browser. Log in and navigate to the connected devices or DHCP client list. Look for the device named after the smart plug's brand or a generic name associated with it.

2. Mobile App: Many smart plugs have dedicated mobile apps that allow you to manage and configure them. The app might display the device's IP address within its settings or device information.

3. ARP Scan: You can use command-line tools like arp or arp-scan (on Linux/Mac) or applications like Advanced IP Scanner (on Windows) to scan your local network for connected devices and their IP addresses. Look for the MAC address associated with the smart plug in the results.

4. Device Information: Some smart plugs have a button or a sequence of actions that, when pressed or executed, can make the device announce its IP address. This method varies by manufacturer and model, so consult the user manual for specific instructions.

Remember, it's important to ensure that you have the necessary permissions and authorization to access and retrieve information about devices on your network.