The rise of the smart devices is a defining feature of our time, but there's one gadget that rules them all: the smartphone.

Smartphones and their apps have made many physical devices redundant to the ordinary consumer. With the dawn of the mobile phone, we saw items like calculators, landline phones, FM radios, and voice recorders replaced.

But older gadgets aren't the only ones being replaced -- in fact, there are modern devices that are already being replaced. Some were even only released a decade or so ago, only to be usurped by apps.

Here are nine modern devices that smartphones are already replacing.

1. White Noise Machines

It's strange to think that white noise machines and white noise CDs were all the rage for a while. Nowadays though, an app can take care of all your white noise needs -- and many of them are completely free.

There are still white noise devices to help you sleep on the market, including ones intended for smart homes. But why spend your money on a device with a single purpose when you can use an app to do it? If you do want something with better audio than your phone's speakers, you can simply cast the app to your TV, Bluetooth headphones, or Bluetooth speakers.

While some white noise apps are very limited if you don't pay for premium features, White Noise Free by TMSoft is actually quite advanced considering they also offer a premium version of the app.

The app even allows you to mix different sounds together into one soundscape, so you can combine the sound of a crackling fire and a thunderstorm together.

Download: White Noise Free (Free)

2. Document Scanners

While document scanners have existed in some form for decades, the consumer flatbed scanner only became an inexpensive, mainstream device in the 2000s. And while you may still want to use a scanner for high resolution scans of images, most document scanning can now be done with just an app on your smartphone.

There are a variety of free scanner apps available that use your phone's camera to create a document scan that has the professional look of a real scanner.

TinyScanner, for example, not only creates PDF documents by using your camera to scan, but it also crops and adjusts the image color and contrast to create high quality document scans.

There are even apps with optical character recognition (OCR), meaning that you can scan documents with your phone, and then still use an app to make the text recognizable and selectable.

CamScanner is a popular scanner app that comes with an OCR feature (with the premium service). It also has a print and fax function that allows you to send your document to the relevant device.

Download: TinyScanner (Free)

Download: CamScanner (Free)

3. GPS Navigation Devices

Relatively soon after GPS devices saw us ditching physical maps, Google Maps and other navigation apps mean that we no longer need our TomTom or Garmin devices. While GPS devices are useful if you need very specific guidance with images on which lane to take, the average person gets the navigation they need from something as simple as a single app.

What further increased the allure of these apps is that they don't require you to pay for extra maps in different regions and then download them onto the device.

Google Maps comes pre-installed on many Android devices, but some users prefer to use other navigation apps. The potential for the app is still untapped by many who use it, as Google Maps has several lesser-known features.

Waze is another popular navigation app, also owned by Google. It comes with traffic information and warnings that help the user choose which route they want to take.

Download: Google Maps (Free)

Download: Waze (Free)

4. Translation Devices

Unless you've studied and used a foreign language, or had a foreign exchange student at your school, you might not have come across translation devices before.

Depending on how advanced the device is, it has various capabilities. Some act as digital translation dictionaries, some allow you to input a phrase in your language that will be translated and read out by the device, and some even translate what you say.

However these devices aren't exactly cheap. Well, not as cheap as the many translation apps now available that achieve similar feats.

Google Translate has provided us with text-to-audio translation for some time, albeit a hit-or-miss affair. It can even facilitate a conversation by converting your audio into a different language and reading it out.

Conversation Translator is another free translation app that translates your speech into text and audio for the target language. While its user interface looks very simplistic, it actually provides translation for an impressive number of languages.

Download: Google Translate (Free)

Download: Conversation Translator (Free)

5. Heads-Up Displays

Heads-Up Displays (HUD) are nifty devices, often used in cars, that cast a display onto your windscreen. Depending on the type of device, this display could be a digital speedometer, GPS navigation, or other dashboard information.

However, even as vehicle manufacturers just started incorporating HUDs into their high-end vehicles, apps with the same function started appearing.

Now there are a variety of HUD apps that serve the same purpose as the original device, except that you place your smartphone on your dashboard instead so that the display reflects onto your windscreen.

However, this is most effective at night. While HUD apps might not be quite as advanced as an actual HUD device, they are an inexpensive option for the average consumer.

Navier HUD 3 is among the highest-rated HUD apps and includes GPS navigation as well as digital speedometers.

Download: Navier HUD 3 (Free)

6. Portable Music Players

Just over a decade ago, everyone was clamoring to get their hands on an iPod. If you couldn't afford one, you might have opted for another brand that offered MP3 devices.

However you might struggle to find people nowadays who have a device that is solely dedicated to playing music. Even the more advanced players that could also play videos have mostly been replaced by apps that play music on our phones.

Users don't even have to download songs anymore in order to play them. With apps like Google Music, Spotify, and SoundCloud, you can simply stream music directly from the apps.

7. Card Machines and Credit Cards

Card machines, along with the cards themselves, are becoming more advanced by the day. But so are the apps that are replacing them.

Android Pay is a popular alternative to contactless credit cards, but there are apps that not only replace your card but also the card machine.

With Snapscan, you simply need to scan a QR code provided by the store you're visiting, and enter the payment amount into the app. The app uses credit card details provided by the user. These stored details are not visible through the app, and you are still required to input a pin into the app to send a payment. The only catch is that it's region-specific, like many other payment apps.

Certain credit card companies, such as MasterCard, provide bank-specific payment apps for clients. Unfortunately, these apps are specific to the brand's cards, whereas other apps are more central and compatible with multiple card brands.

You will need to see which payment apps are available in your region in order to choose the right one for you.

8. Smart Home Hubs

As smart homes and devices became more popular among consumers, the need for a central hub from which to control these gadgets became apparent.

You'll still find many smart home hubs for sale, but many users simply opt to use apps on their phone instead.

As more brands dive into the smart home industry, more apps that act as a central control hub for smart homes are being released.

Samsung Connect is the app that is currently used by the technology manufacturer to control a user's smart devices, with the app connecting to third-party devices as well.

Meanwhile the Google Home app lets you control smart devices like your Chromecast and other Google Home products.

If you have a mix of smart devices from different brands, there are also a few third-party apps that allow you to control them all.

Stringify is a smart home app that connects to over 600 different devices across brands. Wink provides similar functionality, but is hampered by requiring its own hub to act as a link between the app and certain devices.

Download: Stringify (Free)

Download: Wink (Free)

9. Car Keys

While apps that control your car have yet to see mainstream adoption by consumers, the increasing popularity of smart vehicles is resulting in a rise of these types of applications.

Tesla currently has an app that controls the Tesla Model S without the need for car keys. Not only can you drive the vehicle without your keys, but you can also use the app to adjust the car's climate control and track its battery charge.

Nissan also has their own app for their smart vehicles.

As more brands release smart vehicles, you can expect to see even more apps that replace car keys.

Which Apps Are Replacing Your Gadgets?

As our smartphones become more powerful, so do the apps tailored for them. With some of the most powerful smartphones we've ever seen released this year, you can bet that more advanced apps are on the horizon.

It won't be long until we see the replacement of set top boxes, high-end cameras, and other modern devices. You may want to put off purchasing some of these devices, given your smartphone could soon replace them.

Which modern devices are being replaced by apps that you use? Let us know in the comments below.