Espalexa or fauxmoESP "Device Not Found"? Why Emulation Fails and How to Fix It

If you are reading this, you are likely staring at a Serial Monitor trying to figure out why Alexa says “No new devices found” or “Device is unresponsive.”

You’ve probably been using libraries like Espalexa or fauxmoESP. They worked great for years, but recently, they have become hit-or-miss. Maybe they work on your Echo Dot Gen 2, but fail on your Gen 4. Maybe they work for an hour and then disappear.

Here is the technical reason why your emulation is failing—and the reliable way to fix it for good.

The Problem: Local Emulation is Dying

Libraries like Espalexa and fauxmoESP rely on Local Emulation. They try to trick Alexa into thinking your ESP32 is an old Belkin WeMo switch or a Philips Hue bridge.

To do this, they use UPnP (Universal Plug and Play) and SSDP (Simple Service Discovery Protocol) over UDP multicast.

Why this fails today:

Amazon Firmware Updates: Newer Amazon Echo devices (Gen 3, Gen 4, and Show) have significantly stricter security protocols. They often ignore the older, simple UDP broadcast packets that these libraries generate.
Router Blocking: If your ESP device and your Alexa device are on different frequency bands (2.4GHz vs 5GHz) or different subnets, many modern routers block the Multicast packets required for discovery.
No Feedback Loop: Emulation is a “hack.” It is not an official API. When Amazon changes a discovery timeout or a header requirement, your device breaks instantly, and you have to wait for the library maintainer to update it.

The Solution: Cloud Integration (Sinric Pro)

The only way to guarantee stability is to stop tricking Alexa and start talking to her officially.

Sinric Pro takes a different approach. Instead of listening for finicky UDP packets on your local network, your ESP8266/ESP32 opens a secure, persistent WebSocket connection to the Sinric Pro cloud.

When you ask Alexa to “Turn on the kitchen light”:

Alexa talks to the Sinric Pro Smart Home Skill (Official Cloud-to-Cloud integration).
Sinric Pro sends a signal down the open WebSocket to your ESP device.
Your ESP reacts instantly.

Because the connection is outbound from your device, it punches through firewalls and works across different subnets reliably.

Migration Guide: Moving from Espalexa to Sinric Pro

Switching is easier than you think. You don’t need to rewrite your whole logic; you just need to swap the connection handler.

1. The Setup

Espalexa: You define a device name in code.
Sinric Pro: You create a device in the Sinric Pro Portal, get a DEVICE_ID, APP_KEY, APP_SECRET and paste it into your code. This separates your hardware from your configuration.

2. The Code Comparison

Here is a side-by-side look at how you handle a simple light switch.

1. The Old Way (fauxmoESP)

Relies on complex callback comparisons and UDP polling.

#include <fauxmoESP.h>

fauxmoESP fauxmo;

void setup() {
  // ... wifi setup ...
  
  // You had to define devices by string names locally
  fauxmo.addDevice("Kitchen Light");
  fauxmo.setPort(80); // Required for Gen3+ devices
  fauxmo.enable(true);

  fauxmo.onSetState([](unsigned char device_id, const char * device_name, bool state, unsigned char value) {
    // You had to check strings to find which device was triggered
    if (strcmp(device_name, "Kitchen Light") == 0) {
      Serial.println(state ? "ON" : "OFF");
      // Control relay here
    }
  });
}

void loop() {
  fauxmo.handle(); // Must run constantly to catch UDP packets
}

2. The Old Way (Espalexa)

Relies on local discovery loop.

#include <Espalexa.h>

Espalexa espalexa;

void lightChanged(uint8_t brightness) {
   // Control your relay/LED here
}

void setup() {
  // ... wifi setup ...
  espalexa.addDevice("Kitchen Light", lightChanged);
  espalexa.begin();
}

void loop() {
  espalexa.loop(); // Must run constantly to catch UDP packets
}

The New Way (Sinric Pro)

Relies on event callbacks.

#include <SinricPro.h>
#include <SinricProSwitch.h>

#define APP_KEY    "YOUR-APP-KEY"
#define APP_SECRET "YOUR-APP-SECRET"
#define SWITCH_ID  "YOUR-DEVICE-ID" // From Portal

bool onPowerState(const String &deviceId, bool &state) {
  Serial.printf("Device %s turned %s\r\n", deviceId.c_str(), state?"on":"off");
  // Control your relay/LED here
  return true; // request handled properly
}

void setup() {
  // ... wifi setup ...
  SinricProSwitch& mySwitch = SinricPro[SWITCH_ID];
  mySwitch.onPowerState(onPowerState);
  
  SinricPro.begin(APP_KEY, APP_SECRET);
}

void loop() {
  SinricPro.handle(); // Maintains WebSocket connection
}

Why Switch?

Reliability: Works with all Alexa generations (Echo, Dot, Spot, Show, Flex).
Features: Supports dimming, color temperature, thermostats, blinds, and garage doors natively—things that are very hard to emulate with WeMo protocols.
Mobile App: You get SinricPro mobile app to control your devices when you aren’t home (Espalexa only works when you are on the same WiFi).