I was sitting in my car early one November morning, staring at a house across the road.

The darker-than-legal tint on my windows made the suburban setting seem gloomy. The need to stay completely still made it hard to handle the cold morning air.

My camera was switched on and ready to go. I'd used binoculars to check the rego on the car parked out the front. But the curtains were drawn, no lights were on and the property was in a state of disrepair. "This isn't looking promising," I remember thinking.

But wait. There he was. The "claimant" was getting into his car. Got him! Game on.

I followed at a distance through morning traffic until we reached a sport centre on the outskirts of town. I filmed him walking in and when he was out of sight I double checked the grainy, black and white head shot I'd been given.

"Jesus, it's him," I marvelled — I'd been told no-one had managed to catch him on camera.

Over the next three days, I followed and filmed him as he participated in a high-adrenaline sport. He had a long-standing claim for depression and chronic fatigue and the insurance company's claims officer was sure my evidence would "blow the case out of the water".

But a few hours after I submitted the video, I got a call.

"This isn't the claimant. We were aware he had a mate who looked a lot like him, often stayed at his house and borrowed his car. We probably should have passed that on. Just send us the bill."

I was later sent a series of colour photos the company had all along. The mistake was obvious. My work was a waste. This wouldn't be the last time.

The exact number of licensed investigators in Australia is unknown, but insurance work is their bread and butter. ( 891 ABC Adelaide: Brett Williamson )

Is surveillance a good idea?

I spent a year working as a surveillance investigator for some of Australia's biggest insurers from late 2013.

I had wanted to take a break from day-to-day journalism and to gain a few investigative skills that are harder to come by in the media. I completed a short Certificate 3 course in Investigative Services, which is the prerequisite for a licence.

Many of my cases involved people with income protection or disability claims relating to a mental health condition.

The Financial Services Royal Commission recently questioned this practice after hearing evidence about life insurer TAL, and its pursuit of a former nurse with a work-related income protection claim for anxiety and depression.

The nurse was followed and filmed by an investigator going on bushwalks and attending the local pool. Her every move, gesture, kiss was noted down in a detailed report.

In a list of policy questions published after the last round of evidence, the royal commission floated the idea of a ban on this kind of intrusive surveillance.

"Should life insurers be prevented from engaging in surveillance of an insured who has a diagnosed mental health condition, or who is making a claim based on a mental health condition?" the commission asked.

But the Australian Prudential Regulation Authority has tabled a response, arguing that fraud does exist and can, "lead to higher premiums for insurance".

APRA has also warned that if it becomes public knowledge surveillance is off the table, "an inappropriate incentive is created to attempt to take advantage of the circumstances".

'There's something dodgy about him'

There are thousands of private investigators surveilling insurance claimants right now. The exact number of licensed investigators is unknown — most states don't maintain registers — but insurance work is their bread and butter.

It kept me employed full-time for a year — no cheating spouses, no thieves in the night, just people with a claim that was costing their insurance company money.

In each case, I'd ask the claims officer what prompted the decision to track this claimant. Often the reasons were quite subjective.

"Her tone of voice last time we spoke was really suss," one manager told me.

"I just get the sense there's something dodgy about him," said another.

Sometimes the only reason given was that the claim was taking a long time and was expensive. Surveillance was regularly ordered without evidence of a problem.

Those who were "surveillance aware" changed their car behaviour. ( Flickr: Jim Sheaffer )

Looking over your shoulder

The impact was obvious on claimants who were, as we said in the industry, "surveillance aware".

They may have caught an investigator at it, had a lawyer warn them or had already been shown surveillance tapes by claims officers challenging their assertions. With long-term claims this is common.

The result is obvious paranoia and wild attempts to foil investigators even when they aren't sure they're there. I've watched people make a habit of driving 30 kilometres an hour under the speed limit, circling roundabouts four times to see who follows and pulling over after every corner to get a good look at the next car to appear.

Imagine living your life like that, always looking over your shoulder. Now imagine you already suffer from anxiety, depression or schizophrenia and you're under constant pressure from your insurer to "get better".

If an investigator records these counter-surveillance tactics, it can be used to justify further surveillance, even when there's no other evidence. This can result in a vicious cycle of increased surveillance and paranoia.

(For anyone thinking the above tactics will outwit surveillance, they will not help you. Investigators adjust their tactics to compensate.)

What was the success rate?

I followed more than 100 people, clocking up well over 1,000 hours in my car and picked up nine demerit points doing it.

For all my efforts, less than 10 per cent of my targets were filmed doing something that appeared to contradict their claim.

Of course, I did see examples of fraud — some of them breathtaking in their scope and brazenness.

I filmed one man claiming for a shoulder injury working eight hours a day at a building site using a pull-down circular saw. But almost never on a mental health claim.

Claims officers overloaded

Many of the claims officers I dealt with were in their early 20s and handling dozens of claims at a time. One young claims officer told me she had between 80 and 100 claims in her charge.

This often led to situations like the first case I described. I was commonly told to watch the wrong address.

"I haven't seen any movement and I'm concerned they no longer live here," I'd say. "Can you check?"

Without fail, the response would be, "Nah, stick with it. You'll get him for sure!"

Two days would pass and I'd call again. "Are we sure he hasn't moved?"

Begrudgingly, they'd check. "Ah, yeah, actually he moved a couple of months ago. I'll send you the new address and you can start there tomorrow."

Hours wasted. More money on the clock.

Who ultimately pays the price? You'd have to ask your insurer.

Jessicah Mendes is an ABC journalist and private investigator.