What are you thinking when a researcher applies electrodes to your scalp and tells you that the device may change your brain activity? How about if this is a trial to investigate the effect of tDCS on depression? Well - the short answer is that the situation will consciously and subconsciously affect your thinking - the placebo response! It thus is an absolute imperative that tDCS and tACS studies include a "sham" or placebo condition. This makes sure that both participant and study personnel can never be sure if stimulation was actually applied or not.
For this to work, though, you need blinding. One simple way would be to have different devices but that is cumbersome and expensive. More ideally, you have different codes that are linked to the stimulation parameters but the table that lists which code stands for what is locked away. Simple enough? Can your device do this? Can you specify new codes for every study? Can you set them up or do you need to send your device to the manufacturer? Think about it. These are the kind of issues that prompted us to design XCSITE 100. At the heart of it is a table that you can create for your study. Every row in this table contains a code and the stimulation parameters linked to this code. Do you want to do a study where every single person gets a different stimulation paradigm? You got it! You can have as many of these files as you want and you can thus use one device for as many studies as you want at the same time (well, it can only apply stimulation to one person at the time, but you know what I mean).
There are also small other things that make a big difference. Do you want to know if you still have juice in your battery? Of course, you demand that feature for your convenience! But then, hold on, have you noticed that the battery is still almost full after a placebo stimulation session but half empty after a "verum" (real) stimulation session. If you have not noticed, I am sure one of your smart students / research associates / study coordinators has understood this. Now I think this can introduce a major bias in the interaction with study participants, especially in treatment studies. So no, we will not tell you if the battery is half empty or not. We simply give you ten rechargeable batteries and ask you to use a new one for each session and then charge them all together with our nifty 10 bay charger. BTW, whatever device you are using, please do not use one-way batteries for the sake of the environment but of couese first check with your supplier.
There are more examples like that but I am sure you get my point. Let's make sure we use devices that have smart engineering to enable flexible double-blind study designs and that have engineering controls to avoid accidental unblinding.
Think about it!