I've received emails over the years from worried parents asking me how they can monitor the phone use of their teenagers, especially in this age of smartphones with their many different ways of communicating.

Parents are worried about their kids' activities, and they want to be able to keep tabs on them, even if it means monitoring their smartphone activity.

I've been testing software called mSpy that is completely invisible to the phone user but enables the parent (or business owner) to keep tabs on almost all , both incoming and outgoing.

I have to say, it's unsettling to realize this type of surveillance is available, and I'm fairly sure I'm never going to need it.

But for the parents who see their kids slipping into the wrong crowd, I can see why they'd use a product like mSpy.

This disclaimer is on the front page of the company's website: "My Spy (mSpy) is designed for monitoring your employees or underage children on a smartphone or mobile device that you own or have proper consent to monitor. You are required to notify users of the device that they are being monitored."

I would hope employers would notify their employees if this software is installed on company-owned phones.

My guess is some parents tell their kids about the software and some do not.

The software and corresponding subscription start at $40 per month for basic service. There is no contract, but you can prepay for up to a year to lower the cost. A year of premium service is $200. See MSpy.com for detailed pricing and features.

This mobile monitoring software is installed on the smartphone and monitored through a website.

Once the software is on the phone, it's completely invisible to the user.

The monitoring party (parent or employer) logs into mSpy's secure website and sees a dashboard view of phone activities.

The software works on iPhones, Android phones, BlackBerrys and Symbian phones. It doesn't work on Windows phones.

To install mSpy on an iPhone, it must be jailbroken. This is a process where you break open the phone's operating system for the purpose of installing software not sanctioned by Apple. Not every version of iOS can be jailbroken. Consult the mSpy website for specific version compatibility.

The mSpy software monitors just about everything.

The feature set is pretty complete, but not all features are available on every phone platform. Android is a more open operating system, so it supports call recording and keystroke logging. The other phone operating systems don't allow that type of monitoring.

Let's start with phone calls.

MSpy can show a log of all incoming and outgoing phone calls, with phone numbers, call duration and names if the number is in the phone's address book.

Incoming calls from specific numbers can be blocked.

If mSpy is installed on an Android phone, the voice calls can be recorded.

Text messages are logged showing the message content, associated phone number and date/time stamp.

Emails, both incoming and outgoing, are logged with date/time and names if they're in the phone's .

MSpy uses GPS to track the location of the phone and to show a trail of where the phone has traveled within a specified time. The system can also track the phone when GPS is not available.

The mSpy software can also monitor Internet use, showing a complete browsing history with URL, date/time visited and number of times each site was visited.

You can see a list of bookmarks on the phone's browser, and you can block specific websites or block access to specific websites during certain times of day.

Calendar appointments and the phones contact list are also viewable.

Apps installed on the phone are listed in the mSpy control panel. Individual apps can be blocked from running.

Skype chats are readable, and Skype calls are logged but not recorded.

Chats from WhatsApp and iMessage are readable and logged.

Chats from Facebook can be monitored on an Android phone.

The mSpy control panel also shows the phone's photo albums and saved videos.

Photos and videos taken with the phone or downloaded and saved to the phone's storage are viewable, including time and date information.

The mSpy software allows the owner to remotely wipe or lock the phone as well as monitor the battery level and type of network used (Wi-Fi or cellular).

Finally, for the areas of the where monitoring might not be available, there's a key logger for Android phones only.

Key logging is aptly named - it records every keystroke made by the user, and the data is dumped into files that the owner can read through the control panel.

This is scary stuff from a personal privacy perspective, but I suppose if your son or daughter is trying to keep things from you, it's a good way to find out.

I'm torn about mSpy.

The software is easy to use, and it does its job well. I could not find any evidence of the software on the iPhone 5S I tested. The dashboard was easy to navigate and very nicely designed.

I'm glad this software exists for the parents or business owners who believe they need to monitor their children or employees.

I'm also a bit sad that like this exists, for obvious reasons.