Where by “Cheap” I mean low recurring/monthly subscription costs.
I decided to see if I could quickly build something simple myself since I could not find any off the shelf products that matched my needs or budget.
I was looking for a way to implement some kind of notification on my iPhone driven by a PIR sensor based occupancy detector, remote alarm triggering, resilient to power and internet outages (UPS battery backup), without paying huge monthly bills.
My current draft solution is:
PIR sensor -> Arduino -> GSM/GPRS modem Cellular shield -> Prowl iOS App etc.
The GSM shield would also be able to send/receive phone calls and text messages, but I am not sure if I need to use that. For now I will be using the T-Mobile prepaid pay by the day plan with 2G data which costs $2 for unlimited call/text/2G-data only on the days that it is used on, and can be kept alive for 90 days with $10.
The reason for using GSM here is that it will hopefully still keep on working even if the house power is turned off and the internet/phone lines are disconnected as long as the UPS it is powered by doesn’t die. Another useful thing would be to get main power disconnection notification messages using this current sensor.
I will be adding more information here as my plan crystallizes.