How Effective Squirrel Repellents Are?

I'll try to make this straight forward: though there are several types of squirrel repellents in the market today and with different approach in anti-squirrel tactics, it seems no single repellent product is powerful enough to keep the squirrels off from bird food all by itself. Therefore, squirrel repellents can not represent stand alone squirrel proof solution, but they can for sure help as an additional protection to your bird feeder.
This conclusion is backed up by hundreds and thousands of customers who reviewed numerous squirrel repellent products available online.
Let's see first how squirrel repellents work.

Repellent types:

1.Ultrasonic repellents - these are small AC or DC powered electronic devices that broadcast sounds inaudible to human ears, but squirrels just can't stand it and run away. Of course, this theory sounds too simple and too good to be true, so here is the catch: most of the ultrasonic repellents are not squirrel selective and would probably scare the hell of the birds as well! And what's even worse - your cat and dog too! Bad news is also that most of those devices are not "exactly inaudible" to humans and that's what you'll notice in the quiet of the night. So, the general conclusion is that ultrasonic repellents are not only squirrel repellents, but more like animal repellents in general. Therefore, I do not recommend this kind of anti-squirrel defense.

2. Chemical repellents - usually based on coyote urine odor, mothball smell, or some modern synthetic chemical compounds, the very  idea of chemical repellents is to chase away the squirrels from your backyard using squirrel hypersensitive sense of smell. But just like ultrasonic repellents, this type is not squirrel selective and it is very dubious how would certain bird species and your pets react in particular. So, would not dare to recommend this type of repellent either.

3. Food repellents - the point is in adding hot tasting additives to birds food and believe it or not - that might be the best squirrel repellent there is! It's because it is proven to be safe for the birds and the squirrels hate it. Here's how it works: bird's organism is set to be completely immune to hot spicy food while the squirrels just hate Mexican food! So unlike the squirrels, the birds don't feel hotness and do not suffer intestinal consequences from ingestion of the repellent. Secondary benefit of using this kind of repellent is that rats, groundhogs, rabbits and similar rodents also hate hot food.
Also, good news is that you can buy either feeder ready food with repellent already added, or repellent only so you can add to the bird food of your choice.

So, I definitely want to recommend following squirrel repellents: