Say you have a basic plan for power outage monitoring for $3.99 per month (an example). This is the base fee you pay each month. On top of that, you’ll have the cost of text, voice, or WhatsApp alerts — whatever you configure (email alerts are free and text alerts are enabled by default). A text alert costs $0.09 (an example).
You add money to your account upfront, say $30, and the system deducts the daily portion of the monthly fee and any alert charges directly from that prepaid balance.
If you used, say, 10 alerts over two months, then by the end of two months your account balance would be:
Monthly fees: 2 × $3.99 = $7.98
Alerts: 10 × $0.09 = $0.90
Total deducted: $8.88
So your remaining balance from the original $30 would be:
$30.00 − $8.88 = $21.12.