The independent police watchdog is to investigate Wiltshire force's reaction to calls from a man threatening to harm himself, who later died.
Mark Price, 47, made two 999 calls early on 20 May, and officers arrived at his Chippenham address at 0230 BST.
He died in hospital four days later, says the Independent Police Complaints Commission (IPCC).
Investigators would examine if decisions were "reasonable," said IPCC Commissioner Rebecca Marsh.
She said: "The IPCC investigation will specifically look at the second call at about 0110 BST and will try establish whether the decision-making to close the call without a police response was reasonable."
One of Mr Price's neighbours initially called officers at about midnight, expressing concern for his safety.
An ambulance arrived at the address before the police got there and the crew told officers there was no need for them to attend.
At about 0110 BST, police received a call from BT regarding a silent 999 call from Mr Price's mobile phone, but when officers tried to speak to him the call was ended.
When the operator tried calling Mr Price the call went straight to answer phone.
An IPCC spokesman said: "The call was logged and closed by the police control room, who it seems believed it was directly related to the earlier call and therefore did not require a police response."
At 0220 BST the police received a further 999 call from the same mobile number and it appears that Mr Price made threats to harm himself before ending the call.
Attempts were made to contact him, but without success. Officers arrived at the scene 10 minutes later.
Wiltshire Assistant Chief Constable Patrick Geenty said: "The family and friends of Mr Price have my utmost condolences and they will want to be satisfied that everything that needed to be done was done.
"The IPCC will independently investigate the involvement of this force and we will provide them with every assistance.
"Whilst not pre-judging their findings, it is however important to point out that control room operators have to make very difficult decisions and make them instantly.
"It is also right to emphasise that an investigation by the IPCC should not be taken to infer that someone has done something wrong and also that speculation on the eventual findings is not helpful."