The short answer is no, they can pull their PDF ticket up on their phone. However, we will go more in depth below, because you need to ensure you have a 2D barcode scanner if using the desktop check-in apps, and the QR code on the ticket.
We always recommend placing both the QR code and the standard 1D barcode on your ticket templates.
Tickets themselves are nothing more than standard PDF files, and as such are easily handled by any device currently available on the market (computers, smartphones, tablets, etc.).
The answer to this question depends solely on which device you will be using to check the tickets in at your event. If you will be using standard barcode reader (like the one that is used in supermarkets), then customers will need to print out their tickets since these devices cannot scan the barcode from, basically, anything that is not paper. Therefore, it would be wise to instruct customers to print out their tickets before they arrive at the event (for this, you can use the content of an email that is being sent to the customers once they purchase their tickets).
However, if you will be using 2D scanner instead of standard barcode scanner, then you can scan the ticket from the display of the customer's device. Also, Check-in apps for iOS and Android can scan both barcodes and QR codes from both the display and paper.
Of course, if you are still not sure which device you will be using at the time you should start your ticket sales, we recommend you to place both QR and barcode to the ticket template. This way, you will make sure that in either case you have your ticket check-ins covered.
So, with this disadvantage, why on earth would anyone use barcode scanners anyway?
The answer is simple: speed and efficiency.
Check-in apps for iOS and Android devices may be versatile in terms of being able to scan anything from anywhere. But cameras on smartphones are not perfect and depending on the device, there might be problem with focus which will directly result in slower check-ins. Also, one of the key factors is low light condition (which often happens at the door of the event) that also downgrades the performance of the Check-in app on the smartphone.
Barcode scanners on the other hand, are devices with quite a simple mechanism and are in no way affected by any of these factors and as such are much more efficient in scanning.