No matter what industry you are in the American Disabilities Act (ADA) likely has some impact on your business. Accessibility by wheelchairs is one of the more common modifications made.
If you have a business that has two public entrances, in most cases, only one must be accessible. When one entrance is not accessible and another entrance is accessible, a sign must provide direction to the accessible entrance. The alternative entrance must be open during store hours.
If the alternative accessible entrance remains locked due to security concerns, you must provide an accessible way for notifying staff to open the door. A wireless callbox provides a good way to alert staff provided it is located on an accessible route and mounted at an accessible height (generally not more than 48 inches above ground). See this article for more detailed info: ADA Intercom Mounting Requirements
To assist businesses with complying with the ADA, Section 44 of the IRS Code allows a tax credit for small businesses and Section 190 of the IRS Code allows a tax deduction for all businesses. The tax credit is available to businesses that have total revenues of $1,000,000 or less in the previous tax year or 30 or fewer full-time employees. This credit can cover 50% of the eligible access expenditures in a year up to $10,250 (maximum credit of $5000). The tax credit can be used to offset the cost of undertaking barrier removal and alterations to improve accessibility; providing accessible formats such as Braille, large print and audio tape; making available a sign language interpreter or a reader for customers or employees, and for purchasing certain adaptive equipment. The tax deduction is available to all businesses with a maximum deduction of $15,000 per year. The tax deduction can be claimed for expenses incurred in barrier removal and alterations.
Purchasing wireless callbox equipment could be tax deductible, but you will want to seek advice from a tax accountant on this.
The MURS Callbox XT Outdoor Intercom is a good choice for this application since it does not require getting an FCC license and it can communicate directly with two way radios or base station intercoms.