Not sure if this is more of an etiquette or a legal question but...
Suppose that a landlord advertised a rental property in 2020 and mentioned in the ads that it was secured by an ADT security system. The tenants recently renewed for another 12 month lease and have been very happy. Through offhanded discussions with them, the landlord learned that they effectively do not utilize the security system. The inclusion of such system is not explicit (or implicit) anywhere in the lease.
Is the landlord within their legal rights to inquire about whether they use it, so that they may turn it off and stop paying for it if not? Is this rude?