Home security company ADT is suing Amazon subsidiary Ring, claiming its recent designs are a “brazen” copy of ADT’s octagonal blue symbol. The firm cites Ring’s blue octagonal outdoor siren as a recent example. In the filing, ADT lists a dozen of its trademark registrations dating back to the late 90s that feature a combination of blue and octagonal designs, and claims millions of its customers display this symbol to show that their homes use ADT’s security systems.

ADT claims Ring’s use of blue octagons risks confusing customers and misleading them into thinking the two companies are affiliated or associated. In its filing, ADT says “the striking similarity” is evidence that Ring is trying “to reap the benefit of the goodwill associated with ADT’s brand and reputation.” It adds that “this type of confusion seriously undermines the goodwill that ADT has cultivated in its Famous Blue Octagon and irreparably harms ADT.“

As well as the outdoor siren (pictured above), ADT cites an octagonal “Protected by Ring” yard sign that the company started selling in 2016. However, after ADT complained about the sign, Ring agreed to make it less blue, and ADT took no further action at the time.

In the lawsuit, which was first reported by Bloomberg, ADT is asking the federal judge in Florida to order Ring to stop using the allegedly similar symbols in its products, and to pay ADT cash compensation. When contacted for comment, a spokesperson from ADT said that the company “is determined to protect its customers, its employees, and its investors, along with its intellectual property and its reputation.” Amazon did not immediately respond to a request for comment.

The two companies have butted heads before. Back in 2017, before Ring was acquired by Amazon, ADT filed a lawsuit that claimed Ring had benefited from its trade secrets after acquiring a company ADT had previously invested in. The lawsuit led to a judge issuing a preliminary injunction on the sale of Ring’s security system. The two companies reportedly ended up settling the suit the following year for $25 million.

Prior to these legal battles, the two companies had worked together on making their security systems compatible, and ADT showed off Ring’s Video Doorbell working with its security system back in 2016. ADT says it no longer “actively promotes” the Ring Video Doorbell, but will purchase it for customers who want to use it with its security system. However, ADT still advertises that its system is compatible with Amazon’s Alexa assistant.

While its relationship with Amazon’s Ring has faltered, ADT recently received a $450 million investment from Google, which until recently sold a home security system under its own Nest sub-brand. Going forward, Google said it hopes its Nest devices will become the “cornerstone” of ADT’s smart home offering.

Update April 27th, 7:15AM ET: Updated with statement from ADT.