@futurestrader39
My general thinking when a business expense is also a personal expense, and I believe the IRS follows this thinking as well, is the “but for“ rule. But for the business requirement, would you incur the expense?
You can see this rule operate most clearly in the case of a personal vehicle. You are allowed to deduct business mileage for a personal vehicle if you can substantiate that the mileage only occurred because of the business use (by means of a diary, mileage log or other records). You can’t deduct the general expense of owning a vehicle, only the expense that occurred because of the business use.
The other rule is that business expenses must be ordinary and necessary. Ordinary means usual and customary for that type of business, and necessary means necessary for the business to operate, but does not mean essential or indispensable.
So the first question is, is security an ordinary and necessary expense for the kind of business you run. I suppose the answer to that question would be yes these days, for almost any kind of business. Would it be an ordinary and necessary expense for you to hire a guard dog service to patrol your property at night? If the answer to that is yes, then you have to look at the but for question to see if the expenses of your personal pet would also be covered. What expenses do you incur only because of business use, that you would not incur for personal use. (But for the business, you would not have this expense.) Your dog needs food and a dog house and veterinary care even if there was no business purpose. But specific security training for the dog might be something that is only required because of the business.
So I think the answer is probably yes, but the purpose of this very long discussion is to give you the tools to understand how the IRS is going to approach the situation if you are audited. And each case depends on its own unique facts and circumstances.
