Even Simple things are Complicated... in IoT

So, I strive for simplicity in my design.  But I realize that simplicity in design doesn't  mean simplicity in implementation.  Even simple things are complicated when you consider IoT.

Let's take a fairly "simple" example: You want to design a water leak detector for your water heater (or the utility room/closet that hosts it).  Or maybe you are in a flood zone.

This water leak detector should notify you (via your Internet connected Smartphone -- you may not be at home) that there is water present (or rising significantly)on the floor.  Assume that this is VERY IMPORTANT to you because your house is prone to floods or leaks.  Or, you want to make sure your "pump" is doing it's job.

During rainstorms while you sit at work... your mind may wander... to your house... to that damn pump...  Okay, IoT to the rescue!

Simple? Sure. Just throw an ESP8266 or ($10-20) Raspberry Pi at it.

Fine... now let us look at what needs to be done.

1. A water sensor.  Okay, let's assume you found one or threw together a nice one that can be securely mounted to the floor or wall just above the floor.  Basically let's punt on this one. Done.
2. You need Wi-Fi. Chances are you aren't located near an Ethernet port and probably don't want wires everywhere.
3. You need to be battery powered. (Assuming even if you rather plug it into AC, there are flood conditions that could occur during a power loss, right? Like your flood pump isn't working..) So, yes, you need to be battery powered. And the battery should last at least 1 year.
4. You need a cloud server to host the relaying of messages to your Smartphone.

Okay, so you've done all of that hard work or found a nice little sketch/hackaday-device that does all that for you. Done?

Nope.

Here are some issues you need to consider:

1. How do you get notified that the battery is dying?
2. What if someone does an DoS attack (or you changed your Wi-Fi router and forgot to re-configure this device).
3. Speaking of Wi-Fi... How do yo configure this device in the first place?
4. Do you have redundant servers in the cloud. (What if your cloud server goes down?)
5. What do you do if your ISP (or cloud) connection goes away for a few minutes?
6. What if the water sensor is accidentally "detached" (or is damaged)?
7. Is your connection to the cloud secure? Is it authenticated? What if some joker thinks it would be funny to fake out your server into thinking that there is a water leak?
8. What if the device was suddenly "unpowered" (unplugged or batteries were removed). Can you handle that?
9. How do I know, in general, that the device (and my connection to it) is working properly?

Now, you don't have much control over the "Internet" portion of this (realistically). But, at the end of the day, your device will always be blamed. It didn't notify you and your basement is now flooded.

So, let's address some of these issues.  Let's assume that this device is either very, very critical to you (you have lots of water problems and can't afford the massive damage an unattended one would cost) or you want to go to market with this device.

1. How do you get notified that the battery is dying?  
• You are going to have to monitor the battery voltage.  So, some ADC work. 
• And you probably should have a local (loud) buzzer in addition to sending it over Wi-Fi
• LEDs will be next to useless (unless you tend to hang around your utility room/closet a lot)
• Also... Wi-Fi transmission take a lot of power. Consider that in your power budget.
2. What if someone does an DoS attack (or you changed your Wi-Fi router and forgot to re-configure this device).
• Once again, a buzzer. But don't make it too annoying. 
• How (and/or when) do you shut off this buzzer?
3. Speaking of Wi-Fi... How do yo configure this device in the first place?
• Smartphone? Via Bluetooth? As a (temporary) Wi-Fi access point?
• You are also going to need a "rich" app for the phone, or otherwise a nice web server for the device (a web server for a freaking water monitor, ugh)
4. Do you have redundant servers in the cloud. (What if your cloud server goes down?)
• Of course, your ISP can go down... but more likely it will be that $5 per month virtual instance in the cloud that you thought was a really good bargain.
• Consider at least 2 servers (not co-located).
5. What do you do if your ISP (or cloud) connection goes away for a few minutes?
• You are going to need to cache this information and send it later... so you need a "retry" mechanism
• You are probably going to want an event  "date" (or at least elapsed time from). Has it been trying to notify your for hours?
6. What if the water sensor is accidentally "detached" (or is damaged)?
• First you need to detect this. Your monitoring algorithm considers false positives right? Is this a measurement glitch or did the sensor get yanked?
• The sensor (which may just be a couple of traces on a board) needs to have some means of being "detected". So.. it needs to be more than a couple of bare wires or traces on a board.
7. Is your connection to the cloud secure? Is it authenticated? What if some joker thinks it would be funny to fake out your server into thinking that there is a water leak?
• Encryption may not be important (this isn't critical private info), but spoofing can and will be a problem. You will need to some form of SSL/TLS, so you just went beyond your 8 bit Arduino in terms of parts count.
8. What if the device was suddenly "unpowered" (unplugged or batteries were removed). Can you handle that?
• Basically... ask this question if you want to use a Linux based solution (A Pi or Beaglebone). 
9. How do I know, in general, that the device (and my connection to it) is working properly?
• A system check... a heartbeat... an alert to your smartphone that something is amiss
• A heartbeat will affect battery life... be careful.

So... this simple device starts to become complicated really, really fast. Doesn't it?