Espressif device on my network
Espressif is a Shanghai-based chip company that makes low-cost Wi-Fi and Bluetooth microcontrollers.
What Espressif makes
Its ESP8266 and ESP32 chips are the most common Wi-Fi radios in inexpensive smart-home gear. They sit inside smart plugs, bulbs, light strips, relays and switches, including Sonoff and Shelly devices and a large share of white-label gadgets sold under store brands. Hobbyist boards and DIY projects built with ESPHome, Tasmota or Arduino also use them.
What the device on your network probably is
Almost always a small smart-home gadget: a smart plug, bulb, LED strip, light switch or relay is the most likely answer. Less often it is a robot vacuum, air purifier, heater, sensor, or a DIY board someone set up. It is very rarely a phone, computer or TV.
How to work out which device it is
Think about which cheap smart-home gadgets you have set up, then unplug them one at a time and watch which Espressif entry drops off the router list. Many companion apps (Smart Life, eWeLink, Shelly) show each device's MAC address in its device information screen, so you can match it directly. The hostname in your router list is often a giveaway, such as ESP_1A2B3C or a name the app assigned.
Should you be worried
Nothing to worry about in itself: Espressif is the radio chip inside something you or someone in your home plugged in. The name tells you who made the chip, not what the product is. Some budget cameras also use Espressif chips, so if you cannot match it to a plug or bulb, keep unplugging suspects until it goes away.
The app finds every device on the Wi-Fi you are on, at home or in a rental, and puts the vendor next to the hostname, the services it advertises and its open ports, which together usually name the product. Where it cannot tell, it says so instead of guessing. Get RECON for iPhone — one-time purchase, no account, nothing leaves the device.