To make sensors accessible over a wired network we use a DigiSpark MCU. It offers few GPIO pins to connect your sensor(s) to and a USB interface to connect to a server.
If the location you want to monitor already has a physical server in it, the MCU can be connected to it and made accessible over that servers network connection.
If you have a network port available, but no device or if you want to separate existing servers from the monitoring devices, use a small single board system like a RaspberryPi, VoCore, etc. instead. What ever the system, if it has a USB- port and runs Linux, you may use it.
You need access to a wired network connection and a source of power. Some single board computers may offer power over ethernet (PoE) support, which lets you use the network cable as a power source.