This Android app runs on my Samsung GS1 and emails me when my washing machine beeps to indicate that it's finished. It's not very configurable: Beep detection settings are configured in AlarmDetector.kt code. Email is configured via Config.kt (not committed -- Add your own if you want to build it).
Config.kt
package com.rarepebble.audionotifier
const val SMTP_HOST = ""
const val SMTP_PORT = ""
const val SMTP_USERNAME = ""
const val SMTP_PASSWORD = ""
const val EMAIL_FROM = ""
const val EMAIL_TO = ""
const val EMAIL_SUBJECT = "The wash just finished"
const val EMAIL_TEXT = "\n"
Memory allocations have been minimised and it can run for a very long time without problems, however sometimes it does stop working and the phone needs a restart. The app is tagged as a homescreen app, so you can configure it to start automatically on boot and display the log continuously.