Former MI6 agent rates the best and worst spy devices available on Amazon including a lie detector test and rearview sunglasses - and reveals why crisps are the 'best intruder detection system ever invented'

A former spy discussed various spy devices in a video on YouTube channel DEEPREAD MORE: I'm a psychiatrist and these are the common techniques used by liars to conceal deceit

A former MI6 agent has revealed the best and worst spy devices available on Amazon - including a bag of crisps.

Ex-spy Harry Ferguson rated a range of items in a video created by Strong Watch Studios for its new YouTube channel DEEP.

Created by ex-LADbible execs Thom Gulseven and Ben Powell-Jones, the channel publishes two videos a week, each one providing a window into an extraordinary life.

In this clip, ex-spy Harry assessed a range of items, including a 'lie detector test', a stash tin disguised as a Heinz spaghetti tin, and a secret camera detector among other items.

According to the former intelligence officer, his aim was to tell viewers which of these easily-available items 'are actually any use if you want to be a spy'.

Former MI6 spy Harry Ferguson (pictured) rates various spy devices you can buy on Amazon in a video on new YouTube channel DEEP

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Looking first at the stash tin, he said: 'Undo the bottom, and you can hide your secret documents in there. Now, I know what you're thinking "it's pretty rubbish", and you'd be right, but I have actually come across another spy who actually used one of these for real.

'He was an Iranian spy, and we were trying to catch him because he was trying to obtain parts for aircraft, and we were looking for the paperwork for his purchases, and he had hidden them in one of these.'

However, Harry noted, the spy's stash tin was slightly better than the Amazon one. He explained: 'He'd made it him make them yourself out of an ordinary tin. And the reason we found it is because...he'd been quite clever.

'He'd actually crushed it a bit and hidden it in the trash, and we very nearly missed it. I emptied his trash and nearly passed it up. It was only when I checked that I found it.'

The next item he looked at was a secret camera detector that you plug into the charging port of your phone. It emits a red light which is reflected beck when pointed at a lens, so you can find hidden cameras.

'This actually works,' said Harry. 'The problem is, that you have to get right up close to it for it really to work. And if somebody has got a secret camera in your room, they're going to see you going around inch by inch, peering at the wallpaper.'

His third item was a pair of sunglasses which have mirrors in the side, which are supposed to help you see what's going on behind you.

'And they do work - if you put them on....[and] you crane your head a bit, [you can] see what's behind you. So again, seems like a c*** idea, but these are, in fact, based on a device that the CIA used, and they make an important point about counter surveillance.

One of the items Harry looked at was these rearview sunglasses, which help you see what's going on behind you - if you tilt your head at the right angle

'That [is that] when you're trying to spot people who are following you, the idea is to act normally, but then do something that catches them out. That can be a manoeuvre. It can be using a shop window to get a reflection, or even if you did it on a select basis, using a device like this, just to get that glimpse, where they don't expect you to get it.'

Moving onto his fourth item, a lock pick, Harry said it looks like a useful spy device, and that people might imagine spies spend a lot of their time picking locks.

But, he added, they don't, and the main reason is that if you are found in a foreign country with a lock pick, the authorities are 'more likely to think you're a burglar than a spy, but they're certainly likely to arrest you or take greater interest in you'.

In addition, Harry said, you in fact to spend a lot of time practising with modern locks, and that it's not as easy to open them as many of the instructional videos on YouTube make it look.

'And also, most of the places you'll need to get access to as a spy have electronic locks and other kind of locks,' said Harry. 'So the way that spies do it is one of two ways.

'Either they get a technical officer to come in look at the lock and make you a key, or [you use] a skeleton key that will work on that lock so you don't have to do any of this lock picking stuff, or you find a way to actually get a genuine key from one of your agents, and use it like that.'

This stash tin and lie detector test were also evaluated. As Harry explained, lie detector - or polygraph - tests  do not actually work as they only measure different physiological signs of arousal, like heart rate. There are no machines which can detect lies

The next device he assessed was a concealment - something spies can use to hide intelligence they've stolen. The example he looked at looked like a common plug socket, but had a secret compartment at the back that would go into the wall, so to a casual observer, would just look like a normal plug socket.

But, Harry noted: 'Good search teams will test it to see if it works, because they'll be wondering if it's also got a camera in it, or an audio bug - you can also get sockets that will do that. '

Hidden cameras were up next, and the particular one he looked at was in a necklace, but, as Harry pointed out, you can get hidden cameras in all kinds of devices, including hats and pens.

Discussing how useful they are, he said: 'The trouble with all these devices, and I think I've used most of them at one time or another, is that you're usually using them, not so much to record the person who's talking, because you could just use an audio device for that. 

'They do it to make good television, but that's not what spies do. We're not interested in good television. We're interested in data.'

He added that the kinds of data spies are interested in - for example, the numbers on a keypad that somebody punches in - are difficult to film using one of these devices as 'it can be ruddy difficult to actually get the right angle'.

This means that while these devices sound useful, they usually aren't, he concluded. 

Another device that isn't as handy for spies as you might image is this type of small recording device - with the short battery life making them of limited use

Lie detector tests were next on the list. Harry said: 'Their proper name is polygraph tests, because all these tests do is monitor certain outputs from the body, such as blood pressure, respiration rate and so forth.'

He continued: 'The truth is, spies know they don't work. There is no machine that can currently tell if you're lying. None of them reliably work.' 

Looking at more recording equipment, Harry next showed tiny spy cameras, which can be built into items to conceal them - book, tins, or cuddly toys, he suggested.

But, he said, there's always one big problem with these devices - power. 

'Now, the battery in this will stay for about four hours,' He said. 'So if you're hoping to film activity in a location for any length of time, this won't do it. 

'One solution to that is to use something like this, which is actually connected to the mains power. Now this hasn't got video, it's got audio.'

The problems are, he explained, that people will move the items you've hidden recording devices in, and because, if they are connected to the mains power, they will be on the floor, the audio will be terrible.  

While laser traps (pictured) can be a good way to find out if an unexpected intruder has entered a specific room, they come with their own problems, which Harry explained in the video

'You can't just plug them in a room and expect to hear everything, as with all these devices, planning and imagination is what really counts,' he concluded.

The final device Harry rated was a laser trap. These can be used to detect 'if somebody has been into your room, into your office, your hotel room, any premises you want to protect'.

How do spies protect those rooms?

Harry said: 'Well, one way...is with a laser trap, such as this. Now these are so common, these are, in fact, used by children for a game. 

'The idea is...that they shine an invisible laser light that's picked up by a receiver. If you break the beams, then it sounds an alarm or sets off a camera or whatever the particular trap is.'

Again, there are downsides to using these items. 

'The trouble is, if you turn up in Tehran with these in your luggage, chances are they're going to ask some questions,' said Harry.

So what do real spies do? The answer is surprisingly low tech - they use crisps.

According to Harry, crisps are 'probably the best intruder detection system ever invented' - and you get to eat them, as as well use them as a spy device

'Crisps are probably the best intruder detection system ever invented, I kid you not,' said Harry.

'Why are they good? Because you take a crisp, any crisp, and you place it under a rug in the room, or under the door mat, or somewhere where somebody is likely to tread.

'If they tread on it, they'll break it. Now, as you can see, this crisp has a very distinctive shape, once they've broken it, there's no way they're hiding the fact they're broken - even if they rush out and buy another pack of the crisps, they're not going to find a crisp like this.

'If I get stopped going into a country, then nobody's going to question the fact that I've got something like crisps - and the best thing of all is not only does it work to spot whether somebody has come into your room, while you're out, but you also get to eat the crisp.'

You can watch the full video and find out more of Harry's thoughts on these devices, and his real-life experience of using them on in the full video on YouTube.