Email alerts on sensor thresholds in Raspberry Pi

Introduction

We use email alerts to get notified quickly when a sensor detects something important. This helps us act fast without watching the sensor all the time.

You want to know if the temperature in your room gets too high or too low.

You want to be alerted if a door sensor detects it was opened.

You want to get a message when soil moisture is too dry for your plants.

You want to monitor water level and get an alert if it gets too low.

You want to receive a warning if smoke or gas is detected by a sensor.

Syntax

Raspberry Pi

import smtplib
from email.mime.text import MIMEText

# Set sensor threshold
THRESHOLD = 30

# Function to send email alert
def send_email_alert(sensor_value):
    sender = '[e-mail]'
    receiver = '[e-mail]'
    password = 'your_email_password'

    subject = 'Sensor Alert'
    body = f'Sensor value reached {sensor_value}, which is above the threshold.'

    msg = MIMEText(body)
    msg['Subject'] = subject
    msg['From'] = sender
    msg['To'] = receiver

    with smtplib.SMTP_SSL('smtp.gmail.com', 465) as server:
        server.login(sender, password)
        server.sendmail(sender, receiver, msg.as_string())

# Example sensor reading
sensor_value = 35

if sensor_value > THRESHOLD:
    send_email_alert(sensor_value)

Replace [e-mail], [e-mail], and your_email_password with your actual email details.

This example uses Gmail's SMTP server with SSL on port 465.

Examples

This checks if the sensor value is above the threshold and sends an email alert if true.

Raspberry Pi

if sensor_value > THRESHOLD:
    send_email_alert(sensor_value)

This is a simple function structure to send an email alert with the sensor value.

Raspberry Pi

def send_email_alert(sensor_value):
    # email setup and sending code here
    pass

Sample Program

This program checks if the sensor value is above the threshold. If yes, it prints a message about sending an alert email. The actual email sending line is commented out to avoid accidental emails during testing.

Raspberry Pi

import smtplib
from email.mime.text import MIMEText

THRESHOLD = 30

def send_email_alert(sensor_value):
    sender = '[e-mail]'
    receiver = '[e-mail]'
    password = 'your_email_password'

    subject = 'Sensor Alert'
    body = f'Sensor value reached {sensor_value}, which is above the threshold.'

    msg = MIMEText(body)
    msg['Subject'] = subject
    msg['From'] = sender
    msg['To'] = receiver

    with smtplib.SMTP_SSL('smtp.gmail.com', 465) as server:
        server.login(sender, password)
        server.sendmail(sender, receiver, msg.as_string())

sensor_value = 35

if sensor_value > THRESHOLD:
    print(f"Sensor value {sensor_value} is above threshold {THRESHOLD}. Sending alert email...")
    # Uncomment the next line to actually send the email
    # send_email_alert(sensor_value)
else:
    print(f"Sensor value {sensor_value} is within safe limits.")

Important Notes

Make sure to enable 'less secure app access' or use an app password if using Gmail.

Test your email sending code carefully to avoid spamming yourself.

You can replace the sensor_value with real sensor readings from your Raspberry Pi.

Summary

Email alerts help you get notified instantly when sensor values cross limits.

You write a function to send emails using SMTP and call it when needed.

Always test with print statements before sending real emails.

Practice

1. What is the main purpose of sending email alerts when a sensor value crosses a threshold on a Raspberry Pi?

easy

A. To store sensor data permanently in a database

B. To notify the user immediately about important sensor events

C. To increase the sensor's measurement accuracy

D. To reset the sensor automatically

Solution

1. Step 1: Understand the role of email alerts

   Email alerts are used to inform users instantly when something important happens, like a sensor crossing a limit.

2. Step 2: Compare options with this purpose

   Only To notify the user immediately about important sensor events matches this purpose. Options B, C, and D describe unrelated tasks.

3. Final Answer:

   To notify the user immediately about important sensor events -> Option B

4. Quick Check:

   Email alerts = notify user instantly [OK]

Hint: Email alerts are for instant notifications, not data storage [OK]

Common Mistakes:

• Confusing alerts with data logging
• Thinking alerts improve sensor accuracy
• Assuming alerts reset hardware automatically

2. Which of the following Python code snippets correctly sends an email alert when a sensor value exceeds 50?

easy

A. if sensor_value > 50:
send_email_alert()

B. if sensor_value < 50
send_email_alert()

C. if sensor_value > 50
send_email_alert()

D. if sensor_value > 50:
send_email_alert

Solution

1. Step 1: Check Python if-statement syntax

   Python requires a colon after the if condition and indentation for the block.

2. Step 2: Validate each option

   if sensor_value > 50: send_email_alert() has correct syntax and logic. if sensor_value < 50 send_email_alert() misses colon and wrong condition. if sensor_value > 50 send_email_alert() misses colon and indentation. if sensor_value > 50: send_email_alert misses parentheses for function call.

3. Final Answer:

   if sensor_value > 50: send_email_alert() -> Option A

4. Quick Check:

   Correct if syntax + function call = if sensor_value > 50: send_email_alert() [OK]

Hint: Remember colon and indentation after if, and parentheses for function calls [OK]

Common Mistakes:

• Missing colon after if condition
• Forgetting parentheses when calling functions
• Incorrect indentation causing syntax errors

3. Given the code below, what will be printed if sensor_value = 75?

def check_sensor(value):
    if value > 70:
        print("Alert: High sensor value!")
    else:
        print("Sensor value normal.")

check_sensor(sensor_value)

medium

A. Alert: High sensor value!

B. No output

C. Sensor value normal.

D. SyntaxError

Solution

1. Step 1: Analyze the condition with sensor_value = 75

   Since 75 > 70, the if condition is true.

2. Step 2: Determine which print statement runs

   The code prints "Alert: High sensor value!" because the if condition is met.

3. Final Answer:

   Alert: High sensor value! -> Option A

4. Quick Check:

   75 > 70 triggers alert print [OK]

Hint: Check if condition true or false to find printed message [OK]

Common Mistakes:

• Confusing else output with if output
• Assuming no output if condition true
• Thinking code has syntax errors

4. The following code is intended to send an email alert if the sensor value is above 60, but it does not work. What is the error?

sensor_value = 65
if sensor_value > 60
    send_email_alert()

medium

A. send_email_alert() is not defined

B. Indentation is incorrect

C. sensor_value should be a string

D. Missing colon after the if condition

Solution

1. Step 1: Check syntax of the if statement

   The if statement is missing a colon at the end of the condition line.

2. Step 2: Identify the cause of failure

   Without the colon, Python raises a syntax error and the code won't run.

3. Final Answer:

   Missing colon after the if condition -> Option D

4. Quick Check:

   if statement requires colon [:] [OK]

Hint: Always put a colon after if conditions in Python [OK]

Common Mistakes:

• Forgetting colon after if condition
• Assuming function is undefined without checking syntax first
• Thinking sensor_value must be string

5. You want to send an email alert only once when the sensor value crosses above 80, not repeatedly while it stays above 80. Which approach is best to implement this on a Raspberry Pi?

hard

A. Restart the Raspberry Pi after each alert to reset the sensor

B. Send an email every time the sensor value is checked and above 80

C. Use a flag variable to track if alert was already sent and reset it when value goes below 80

D. Ignore sensor values below 80 and send emails continuously

Solution

1. Step 1: Understand the problem of repeated alerts

   Sending emails repeatedly while the value stays high can spam the user.

2. Step 2: Use a flag to send alert only once

   A flag variable remembers if alert was sent; reset it when value drops below threshold to allow future alerts.

3. Final Answer:

   Use a flag variable to track if alert was already sent and reset it when value goes below 80 -> Option C

4. Quick Check:

   Flag variable prevents repeated alerts [OK]

Hint: Track alert state with a flag to avoid repeated emails [OK]

Common Mistakes:

• Sending emails every check causes spam
• Restarting device is inefficient and unnecessary
• Ignoring values below threshold misses reset opportunity